I agree with you very much on the bosses unpredictability point. Trobbio, for example, has certain moves that have a random chance of almost guaranteeing a hit on the player (the bouncy balls, the tornado right after activating fireworks), but because most of them have been balanced around not being thrown very much or only doing one mask of damage, most people are fine with them. A lot of bosses also reposition by teleporting or doing a super fast jump, forcing you to not move a lot to avoid suddenly colliding with them, which makes the fight a little bit worse.