What do I mean when I say that PbtA isn’t a game system, it’s an approach to system design?
First we have the D&D approach to system design: races, classes, levels, hit points, you know the one.
Next we have the GURPS approach, which I guess was actually spearheaded by Champions: skill-based, point-buy, with an expansive description of your character’s competencies in any number of situations, and a limited set of mechanisms for testing them for success and failure.
Not pictured is the Forge approach, which appears in several of my games pre-Apocalypse World: a more-or-less specified situation of conflict, freeform character traits, and a universal conflict resolution system.
PbtA represents an approach to RPG design as broad as any of these. Choose two given PbtA games, and you shouldn’t expect them to be any more similar than two point-buy games or two Forge games.
PbtA isn’t a system you can adapt to different genres, like GURPS, d20, Fate, One-Roll Engine. It’s an approach, a framework, a vocabulary for designing new systems that work how you want them to work.