How Armageddon got past testing I'll never know
I don't hate the concept of a boss fight that gives you more boss bags if you do well. It's nice for Skeletron, who you otherwise can't fight again without killing the clothier. I think the main problem with it is that "no hit" is really silly for bossess that spam indiscriminate projectiles. The Destroyer releases all those probes and lasers, especially in "Revengance", and even if you know what you're doing you may get tagged once or twice by stray fire - it's okay normally because they don't do a lot of damage but if it's instant-kill, it's instant kill.
I think the main issue is that Terraria itself just isn't designed around high octane boss battles. If you pay attention, you'll notice a lot of the best weapons are crafted from enemy drops, or farmed from field enemies directly. Up until the Moonlord you tend not to be farming a boss for that level's top equipment, except for of course the Wall of Flesh to obtain your class emblem. The mechanics for fighting bosses aren't amazingly tight, so making a standard boss fight more challenging is a difficult proposition.
Something else I questioned is the introduction of... weapons that deal percentage damage
See, and this is what I actually don't get. Sure, the Daedalus Stormbow is pretty powerful against the Destroyer if you farm a bunch of holy arrows, but to use it at that level you have to spend a lot of time killing pixies and unicorns for the ammo. So Calamity nerfs the bow
and holy arrows, but turns around and gives you the Halibut Cannon, and now guns that do percentage damage to specific bosses. What exactly is the message here? What am I supposed to be taking away?
Because if the message is that Fabsol doesn't trust me not to use the Stormbow on the Destroyer, why does he trust me not to use the Halibut Cannon on it? Obviously it's not an issue of feeling players are forced to the weapon. Does he think the Stormbow has too much longevity? Well clearly not, because guns that do percentage damage can last all game, and by design the Halibut gets stronger as the game progresses.
Calamity cuts off vanilla things, nerfs their mechanics, but then introduces a much worse design philosophy with its own weapons and equipment.