While I don't have definitive proof I've seen both AI fanarts that are so good it's hard to tell if it's AI or not and AI abominations that are so bad and artificial it want to make you puke so I guess it really depends on the model.

Funny enough adobe now offers AI generated stock photos that are closer to those abominations rather than anything good. Though if you think about it AI stock art is so pointless... There are already so many stock photos you can choose from. Why would you go out of your way to choose a photo that looks almost the same as regular stock photos but people have 4 arms in it...