The lower cost is not the bad thing. Allowing an AI to learn from it and regurgitate is the bad thing. If we can put anything into an AI and then say whatever it spits out is "clean", even though it is obviously imitating what it learned from, whoever puts the investment into trying something new becomes the sucker.
Also, I don't get this weird sense of entitlement people have over someone else's work. Just because it can be copied means it should belong to everyone?
Can you please explain how did you jump to this conclusion?
I fail to see how artistic expression would cease to be a thing and how people will stop liking novelty. And as long as those are a thing, original styles will also be a thing.
If anything, making the entry barriers lower would result in more original styles, as art is [at least] frequently an evolutionary process, where existing ideas meet novel ones and mix in interesting ways. And even for the entirely novel (from-scratch, if that's a thing) ideas will still keep appearing - if someone thinks of something, they're still free to express themselves, as it was always the case. I cannot think of why people would stop painting with brushes, fingers or anything else.
Art exists because of human nature. Nothing changes in this regard.
It means art can get more ambitious. Ghibli made their mark, and made their money. Now it's time for the next generation to have a turn.