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.
Normally I'd agree, but we have shadowbans, which really irks me.
Almost everyone banned on HN is banned publicly, with a public message explaining why.