I agree there is a dichotomy. I personally think AIs are better debaters than humans, at the very least in their ability to make less logical mistakes and have wider knowledge. I would suggest everyone should run their thoughts through an AI to get a constructive critique, it would certainly reduce lot of time wasted.
And I find the decision to "ban" AI slightly ironic, when HN has a disdain (unlike its predecessor Slashdot) for funny or sarcastic comments, which require the reader to think more, rather than having a clear argument handed on a silver platter. I mean, it is what truly human communication is like - deliberately not always crystal clear.
I suspect that HN will eventually be replaced by an AI-moderated site, because it will have more quality content.
There are huge advantages to AI-moderation. TBD what the unintended consequences are. But I think it's worth trying.
I believe banning AI is a temporary solution. Even today it is very hard to tell human from AI. In the future it will be impossible. We are in the Philip Dick future of "Do Androids Dream" (the book, not the movie). Does it matter if we can't tell human from AI? The book proposes that how we feel about the piece we're reading is the only thing that matter. How the piece got created is irrelevant.