I get where you're coming from. I'm going to mention though, that in practice... well, here's an example: the Binding Coil's Turn 2 lets players go through it in several different ways, adjusting the boss as a result of what the players do. What happens? Everyone takes one specific path, every single time.

Now, if you want to talk "sometimes these bosses are different" or "different mob groups spawn here" or "here's these puzzles that take different solutions each time", sure, I'm totally down for that.