Have you ever actually looked into people who do that? They put in a lot of effort into understanding the original creator, their intent, process, materials etc. The copies are still very much art as they are expressions of the imitator's feelings towards the work. Performing studies of popular art by trying to replicate it is a powerful tool for learning precisely because it allows you, as an artist, to understand how the original artist thought, helping you learn to think like an artist and leading you to develop your own ideas and means of expression.
How do we know? We can do art Turing Test - have 3 real artists and an text/image generation AI train on somebody's art. Have it generate the images and answer questions about the art.
If you can't tell which one of them is AI - would you conceed they are "all of that"?
The claim that people don't copy art styles or even that it's rare is ridiculous. Opwm tumblr and you will immediately be presented with a counterexample.
I mean if you're talking about throwaway 4chan/twitter-anime, that's a different tier of art. I'm talking artists more like Jeremy Lipking or Jose Lopez Vegara.
AI is none of that.