I've also noticed that very obviously LLM-generated comments are called out, and the community tends to agree, but those that have any plausible deniability are given far too much leniency, and people will over-index on the guidelines to give them the benefit of the doubt.
I don't think a captcha is the solution, as it'll degrade conversation by an OOM though.
I'm still amazed at how Reddit weaponized the block feature.
If you block someone, you not only can't see their posts, but you ice them out from replying in the rest of the thread.