Two Sets of Rules, the Good and Bad?

[Morty]

I can't speak for its execution in 5E specifically, but in general I don't place much value on PC/NPC asymmetry. Rules are abstractions and I don't see why everyone in the world should use the same abilities in the same way. Especially in D&D, where character creation is laser-focused on a very specific type of character. Using PC classes and levels for non-adventurers gets silly pretty quickly.

Legendary actions seem like one of 4E elements that made it to 5E but were cut up and diminished to make them acceptable. Still, they're a necessity for running proper boss fights, one way or the other.