I do want to note that I can appreciate the value of narrative justifications for fantasy powers as a set of worldbuilding tools.
I like that there can be a whole portfolio of reasons for a character to gain the ability to do something fantastic. Demigods, dragon-touched, and demonspawn are all completely cromulent character concepts to me.
I simply do not think they need to be coded into the levelling mechanics of the game. I think that doing so limits the game unnecessarily.
Though.. with that said, I think it'd be interesting if the game baked more consideration into the specifics of how PCs get the power ups that they do. If, instead of leveling and getting whatever the book says they get, they could quest for powers.
You want to fly -
go see that alchemist or
perform x ritual at that temple,
bargain with that fey,
get x magic item from y enemy.
Like, if the concern with leveling is how we're handwaving the narrative, maybe we could just take a narrative approach instead.