Besides the pilots (and maybe the menus), there is IMO nothing cartoonish with Fusion.
I have to say that every WipEout after Fusion looked much more cartoonish in-game than Fusion does. In terms of realistic-looking WO3 and WOF are probably the most believable.

And yeah, even WOHD looks cartoonish on some tracks. Too much color. Too much neon. Things that next-gen graphics can't fix