Gentoo bans AI-created contributions

This is absurd. The value of a copyrighted work is not dependant on the amount of effort that went into it.

If anything LLMs are a great equaliser. It used to be that to be a great writer you needed to have a great idea for a story and the skill to execute it. Now people with a great idea but not quite as good writing skills get a chance they might not otherwise.

Copyright protects the economic value and moral value of a work. The fact that other people can now also create new works easier does not reduce the value of copyright at all (or break it). Copyright does not protect all uses of your work, only those that reduce the economic value of the original.

This is prosaically true in the sense that it's ultimately a judgment call on the part of the trier of fact, but as a matter of law, there absolutely is an answer, and the law generally expects you to know it. You can wave your hands about copyright "breaking" all you want, but the legal system is not going to be impressed.

You are correct, however, that AI does put the legal system in a bit of an awkward spot. Up until now, derivative works have been decided by the trier of fact (judge or jury) looking at the original and the allegedly infringing work side by side, and seeing if they're close enough that copying can be inferred. The legal term used in the US is "substantially similar" (or "strikingly similar"), but most countries are going to use a similar method in their courts.

That works fine when you have one original. When you have two billion originals, and an unbounded set of potentially infringing works, it's a bit impractical. Right now, the unspoken expectation is that the plaintiff has to do the leg work of figuring out which images to put side by side in this comparison (US courts would say the plaintiff is "master of their complaint" and thus responsible for deciding exactly what is and is not in scope). That's not easy in the case of AI, and it's the main reason (or at least, a major reason) that artists have struggled to sue image generators successfully.

But that does not imply that an image generator "erases" copyright as you have put it. If an artist is able to find a specific infringing output that closely resembles their art, and their art was used as a training input, then the artist might have a case. Saying "the AI breaks copyright" is not going to be an effective defense.