I wouldn't mind if playing solo balanced the game a bit differently, but in most cases I don't have a problem.
I regularly play this game alone since dealing with other people can frustrating. I play normal alone typically, but I never start to struggle until I get to Moon Lord level stuff, and it's usually because I'm trying to do class-lock style themes and it tends to be a pita.
That said, I cannot solo on expert yet, not feasibly from scratch... although, I have done expert on online playthroughs and they make for an exciting game.
The problem with playing online, though, is that I enjoy 'fresh start' servers and they tend to last literally weeks of constant gameplay and focus. I have to both be there constantly, AND moderate the stupidity that inevitably comes with it. I have to constantly watch for griefing, catch people trying to cheat, and keep things in line all along the idea of having a good time. Hard to do without close friends, and not many of the people I used to Terraria regularly with still play.
Either way, I disagree that this game needs an 'easy' mode. You simply need to be a little more creative. There are no bosses in this game that are impossible to solo by any stretch of the imagination, though some can be very hard, especially if you limit yourself. I'll openly admit that Moon Lord (and Duke Fishron) are pretty scary. But with the right strategy, like any other boss, they are totally doable, and without exploiting a cheesy tactic to win.
Again, the best I can say is that I wouldn't be against the game rebalancing a bit around a single player -- especially on the consoles -- but it's not really necessary. I'm not that great of a player, and I can handle this stuff pretty easily. Look up some guides and create a good strategy. Drink some potions, get buffed. With the right preparation, anything in this game can be relatively easy.