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.
news.ycombinator.com##:matches-path(/^/item\?id=/) tr a.hnuser:has-text(/^dpifke$/):upward(tr)
This mostly works, but only kills the user's comments and not replies, so it sometimes can be confusing. news.ycombinator.com##.default:has(a[href="user?id=dpifke"]) .comment