Wow! I feel like I just read the Split Attraction Model of the Fanfic world.
I can definitely see how the different AU types are distinct, and also how they could blend and overlap within a fic.

I originally got into fanfic for the fix-its. There was a point where you could tell the original content creators weren't brave enough, or were threatened or simply decided to viciously haul the plot away from where it was growing naturally.
Yeah, the author is dead, long live the author's properties!