If I tell you something I learned from a copyrighted book, I am not doing something illegal.
If I produce a copy of someone else’s output and state it’s my own, I am. That’s plagiarism. And I think this is the best way to view AIs that create artworks “in the style of” etc — as plagiarism for output, not copyright violation for input.
I, and I am the author of several things including proprietary software (published, sold, even acquired!) and a novel I hope to publish soon, increasingly think copyright is an evil. I like getting income from what I make but I don’t believe in stopping people accessing what I create. Using it to restrict learning absolutely is an evil. And an AI uses it to learn.