The purpose of intellectual property is to give an incentive to produce new knowledge (and art) by giving the inventor a way to monetize their work. Arguably this does not particularly work; but if you accept the argument then it seems to generalize fairly cleanly to AI. It's giving people an incentive to point their AIs at problems they're familiar with, and do the work to publish a solution for everyone, not just a hacked-up fix for themselves.
If certain inventions become very easy for AI models to discover, i.e. the discovery bound to happen, then in these areas it becomes a game of land grab.
True, but that is plausibly covered by existing precedent: If a discovery is "obvious to one skilled in the art", it can't be patented. IANAL but this seems to me easily extensible to "if you can do it in two five-minute prompts you can't patent it".
Separately, land grabs are not necessarily economically bad. The land being grabbed gets into productive use fast, and the grabber is hardly going to get all the resulting value. Especially not when the monopoly is temporary, as with a patent.
It's already been decided that generated content is not copyrightable
Yes, but the discussion was about patents.
"Knowledge (and art)"... got any examples of patents approved that were llm generated?