Most of that art is being created irrespective of copyright, though. Much of it uses exceptions to copyright and some is straight up in violation (most "fan art"/fanfiction). It's either not monetised or monetised through things like Patreon.
I wouldn't say we have more "traditional" art that an author spends time creating with the vision of selling copies for years to come, than we did when copyright terms were shorter.
I doubt that's true.
Is there a lot of fan art, yes, there's also massive amounts of original works as well. There is no lack of either.
I don't have any numbers on fan art vs original works floating around the web, but even those original works aren't being monetised via copyright. They would be created even if copyright was abolished or significantly weakened.