To start this suggestion, let's just go over all the classes and see their attributes and pitfalls.
Melee:
Defence: Highest
Attack/DPS: High, potentially highest
Weapon reach: Mostly high, despite the name.
Ammo: None
Weapon control: High
Ranged:
Defence: Medium
Attack/DPS: High, potentially highest
Weapon reach: High
Ammo: Arrows, Bullets, rockets, amongst others, as well as none occassionally
Weapon control: Medium
Magic:
Defence: Low
Attack/DPS: Medium
Weapon reach: Low to high
Ammo: Mana
Weapon control: Low to high
Summoner:
Defence: Extremely low
Attack/DPS: Extremely low (excepting whips, more on that later)
Weapon reach: High, but really quite low.
Ammo: Mana, but not as applicable
Weapon control: Extremely low (excepting whips)
By these standards, Melee wins in every single category, and Summoner loses in almost every category. The difference between the classes is horrendous. Clearly there needs to be some sort of revolution to create more equality between the classes. So I'm going to go over every category and suggest some balance changes to make the game more balanced.
Melee:
Melee should definitely keep its high defence; it's supposed to be an up-close and personal class. However, it has no right to have such high-range, high damage weapons such as Yoyos and projectile swords. Using yoyos means that you barely need to be close to enemies for the entire game, and even without them, by hardmode you're going to be using melee weapons for their ranged capabilities regardless regardless. I don't believe that these weapons should be removed of course, and a straight-up nerf wouldn't work either. I just think that the ranged projectiles should be nerfed, so that melee is encouraged to be an upclose battle again rather than just a better version of ranged/mage. And Yoyos have desperately needed a nerf since their conception. They are brokenly powerful, and with them you can easily win the entire game (my yoyo-only run was by far the easiest run I've ever done).
Also, one hidden feature of mastermode is a scaling defence bonus. In normal mode, incoming damage is reduced by 50% of your defence stat. In Expert mode, that increases to 75%, and in Master mode, it's 100%. This is good for balancing out the difficulty of these modes, but it does absolutely nothing for low defence classes. And of course, what classes give high defence? Melee. Melee gets even more ridiculously overpowered in Mastermode.
Ranged:
I think ranged is probably one of the best balanced classes. However, I do believe that their defence should be lower than magic and summoner classes, as they are the ranged class, and so should be expected to be hit the least, as well as slightly increased attack.
Magic:
Magic can have its good moments. But for the most part, it has measily attack, the added cost of mana, and terrible defence. For a class which requires mana to fire, I expect much higher attack than they currently have. I also believe that a class which can have both high range and low range, but in general lower than ranged, should have a higher defence. I haven't played a mage playthrough in a long time because it is generally unsatisfying. You expect a mage to have high damage potential, but even with the best armour and weapons, you tend to do less damage than the ranged capabilities of melee.
Summoner:
sigh...
I had the displeasure of playing summoner on my first playthrough of mastermode (and only, unless the mode gets better). And I couldn't believe that somehow summoner had became even worse than it was in 1.3. In 1.3, it felt like a feasible class to play as. It was a challenge, yes, but it was fun. And now, you have a choice.
1. Use actual summoning weapons and be absolutely awful
2. Just use the whip and become a lesser melee
Minion AI is absolutely horrendous. Most of them will prioritize being close to you over actually attacking the enemy. There's a reason why people use the blade staff (other than its piercing) for practically every boss until you get Terraprisma or Stardust dragon, and it's because most other minions simply don't attack bosses. Couple the bad AI with low attack and defence in general, and you've got a terrible class.
Now let's talk about whips. Let's be honest: they are melee weapons. This isn't inherently a bad thing, but it needs to be correctly done in order to add to the summoning class and not subvert it. This was not achieved in the 1.4 update, and was worsened in the 1.4.1 update. Whips are not in fact the supporting weapon that they should be to fit in with the summoner class, but have become THE weapon of the summoner class. No longer is using actual summoning weapons useful, because now you can just use obsidian armour and whips and beat half the game.
How do I think things ought to be with summoning class? Firstly, whips should do barely any damage by themselves. The entire purpose of the summoning class is that you stand back while your minions do all the damage for you, and hence this is why summoner has such little defence. They are supposed to be a ranged class. But then the melee whip comes in and forces players to be extremely close to their enemies in order to make any feasible attacks. With such low defence, this means you die a lot. What I believe is the solution is to make the whip effect last maybe 10-15 seconds, and make the whip attack far lower. This means that you will swing by the boss every 10 seconds to get that extra buff, and then you can hang back again to let your minions do the work.
Also, another thing which made summoning way worse in 1.4 was the removal of being able to switch out accessories and have your minions keep their buffs. This pointless nerf made the worst class even worse, and took out half of the strategy.
General:
I also believe that hardmode terraria forces the player far too much to abide by one of the 4 classes. Excepting a few, armor sets focus in too much on a single class. And those which don't specify still group together other classes, such as Frost and Forbidden armor. I believe this system doesn't actually line up with what a first time player wants to do, as they will use the items they pick up along the way and want to use them regardless of their armour. Therefore, I think that some more generic armor sets which don't adhere to one class is necessary. Crystal Assassin armor is a good example of this, however its low defence means that you'd probably have better armor to fight Queen Slime regardless. I also think Frost and Forbidden armor is a great idea, but I think Melee+Ranged and Magic+Summoner are balance-wise poor combos. Melee and Ranged are 2 opposing classes, quite literally a ranged and a close class. Magic and Summoner do work better together, but I think a better combo is Ranged and Summoner, as both are ranged classes, and Magic and Melee, as they are a mix of ranged and close-combat.
None of this is mentioning how awful PVP is. Summoner minions literally will not attack players, meaning that only whip can be used. Other than that, melee absolutely strikes out over all. Just use a projectile sword and get them cornered and the fight is won.
If you got this far, thank you! Despite 1400 hours in Terraria, I feel this, amongst other 1.4 problems, has really affected my enjoyment of the game, and I won't be returning until some major fixes occur. I might post some more suggestions with my other problems with the current state of the game, but I think others have pointed a lot of them out already.
Melee:
Defence: Highest
Attack/DPS: High, potentially highest
Weapon reach: Mostly high, despite the name.
Ammo: None
Weapon control: High
Ranged:
Defence: Medium
Attack/DPS: High, potentially highest
Weapon reach: High
Ammo: Arrows, Bullets, rockets, amongst others, as well as none occassionally
Weapon control: Medium
Magic:
Defence: Low
Attack/DPS: Medium
Weapon reach: Low to high
Ammo: Mana
Weapon control: Low to high
Summoner:
Defence: Extremely low
Attack/DPS: Extremely low (excepting whips, more on that later)
Weapon reach: High, but really quite low.
Ammo: Mana, but not as applicable
Weapon control: Extremely low (excepting whips)
By these standards, Melee wins in every single category, and Summoner loses in almost every category. The difference between the classes is horrendous. Clearly there needs to be some sort of revolution to create more equality between the classes. So I'm going to go over every category and suggest some balance changes to make the game more balanced.
Melee:
Melee should definitely keep its high defence; it's supposed to be an up-close and personal class. However, it has no right to have such high-range, high damage weapons such as Yoyos and projectile swords. Using yoyos means that you barely need to be close to enemies for the entire game, and even without them, by hardmode you're going to be using melee weapons for their ranged capabilities regardless regardless. I don't believe that these weapons should be removed of course, and a straight-up nerf wouldn't work either. I just think that the ranged projectiles should be nerfed, so that melee is encouraged to be an upclose battle again rather than just a better version of ranged/mage. And Yoyos have desperately needed a nerf since their conception. They are brokenly powerful, and with them you can easily win the entire game (my yoyo-only run was by far the easiest run I've ever done).
Also, one hidden feature of mastermode is a scaling defence bonus. In normal mode, incoming damage is reduced by 50% of your defence stat. In Expert mode, that increases to 75%, and in Master mode, it's 100%. This is good for balancing out the difficulty of these modes, but it does absolutely nothing for low defence classes. And of course, what classes give high defence? Melee. Melee gets even more ridiculously overpowered in Mastermode.
Ranged:
I think ranged is probably one of the best balanced classes. However, I do believe that their defence should be lower than magic and summoner classes, as they are the ranged class, and so should be expected to be hit the least, as well as slightly increased attack.
Magic:
Magic can have its good moments. But for the most part, it has measily attack, the added cost of mana, and terrible defence. For a class which requires mana to fire, I expect much higher attack than they currently have. I also believe that a class which can have both high range and low range, but in general lower than ranged, should have a higher defence. I haven't played a mage playthrough in a long time because it is generally unsatisfying. You expect a mage to have high damage potential, but even with the best armour and weapons, you tend to do less damage than the ranged capabilities of melee.
Summoner:
sigh...
I had the displeasure of playing summoner on my first playthrough of mastermode (and only, unless the mode gets better). And I couldn't believe that somehow summoner had became even worse than it was in 1.3. In 1.3, it felt like a feasible class to play as. It was a challenge, yes, but it was fun. And now, you have a choice.
1. Use actual summoning weapons and be absolutely awful
2. Just use the whip and become a lesser melee
Minion AI is absolutely horrendous. Most of them will prioritize being close to you over actually attacking the enemy. There's a reason why people use the blade staff (other than its piercing) for practically every boss until you get Terraprisma or Stardust dragon, and it's because most other minions simply don't attack bosses. Couple the bad AI with low attack and defence in general, and you've got a terrible class.
Now let's talk about whips. Let's be honest: they are melee weapons. This isn't inherently a bad thing, but it needs to be correctly done in order to add to the summoning class and not subvert it. This was not achieved in the 1.4 update, and was worsened in the 1.4.1 update. Whips are not in fact the supporting weapon that they should be to fit in with the summoner class, but have become THE weapon of the summoner class. No longer is using actual summoning weapons useful, because now you can just use obsidian armour and whips and beat half the game.
How do I think things ought to be with summoning class? Firstly, whips should do barely any damage by themselves. The entire purpose of the summoning class is that you stand back while your minions do all the damage for you, and hence this is why summoner has such little defence. They are supposed to be a ranged class. But then the melee whip comes in and forces players to be extremely close to their enemies in order to make any feasible attacks. With such low defence, this means you die a lot. What I believe is the solution is to make the whip effect last maybe 10-15 seconds, and make the whip attack far lower. This means that you will swing by the boss every 10 seconds to get that extra buff, and then you can hang back again to let your minions do the work.
Also, another thing which made summoning way worse in 1.4 was the removal of being able to switch out accessories and have your minions keep their buffs. This pointless nerf made the worst class even worse, and took out half of the strategy.
General:
I also believe that hardmode terraria forces the player far too much to abide by one of the 4 classes. Excepting a few, armor sets focus in too much on a single class. And those which don't specify still group together other classes, such as Frost and Forbidden armor. I believe this system doesn't actually line up with what a first time player wants to do, as they will use the items they pick up along the way and want to use them regardless of their armour. Therefore, I think that some more generic armor sets which don't adhere to one class is necessary. Crystal Assassin armor is a good example of this, however its low defence means that you'd probably have better armor to fight Queen Slime regardless. I also think Frost and Forbidden armor is a great idea, but I think Melee+Ranged and Magic+Summoner are balance-wise poor combos. Melee and Ranged are 2 opposing classes, quite literally a ranged and a close class. Magic and Summoner do work better together, but I think a better combo is Ranged and Summoner, as both are ranged classes, and Magic and Melee, as they are a mix of ranged and close-combat.
None of this is mentioning how awful PVP is. Summoner minions literally will not attack players, meaning that only whip can be used. Other than that, melee absolutely strikes out over all. Just use a projectile sword and get them cornered and the fight is won.
If you got this far, thank you! Despite 1400 hours in Terraria, I feel this, amongst other 1.4 problems, has really affected my enjoyment of the game, and I won't be returning until some major fixes occur. I might post some more suggestions with my other problems with the current state of the game, but I think others have pointed a lot of them out already.