Isn't there a middle ground where there is a baseline "script," but the ability of players to interact with the boss beyond chip damage impacts how the fight plays out?
Like tanking in many of the new boss fights seems unnecessarily limited. Point the boss north. Okay. Oh look it's now jumping across the stage! And things from beyond the arena are throwing rocks at me.
There's no reason in principle why we could not stun, silence, interrupt, heavy, knock back, blind, bind, poison, yeet... the boss. Similarly for anything appearing at the side of the arena. Strikes me as far more interesting and would justify having 30 buttons.