Except several of the creators of those shows never went to CalArts. Ben Bocquelet didn't. Rebecca Sugar didn't.
Fuck, you could morph that headshape into Mickey Mouse. That doesn't mean Walt suffered from "CalArts style".
Bugs Bunny's design is literally based off the most generic long bean bodyshape that there was in early cartoons.
The reason that headshape is so common because it's a quick and recognizable way to draw likeable children.
Which may be why Rory's art is so fucking weird, because instead of trying to draw recognizable features, they throw a bunch of mismatching shit together and call it diversity.