I fear that a reply like this can come across as dismissive, but you have to understand that people have been saying that the quality of HN has been falling ever since HN started 15 years ago. There's a strong bias (if not several biases combining) to feel like it's always getting worse. Since people are saying this all the time, it's hard to give much weight to a bare statement along those lines. Positive generalizations aren't that different, btw. The main thing I've learned is that everybody overgeneralizes. Most likely we're hard-wired for it.
Because of that, specific examples actually carry more weight. The case you're describing sounds like someone it is really bad for HN to lose. But I'd need to see links.
Internet forums are super weird and there are limits to what one can do about it. I wish it weren't so. The way that large online group dynamics interact with individual psychology is bizarre, and often leaves people feeling wounded and aghast (I've tried writing about this a few times, e.g. https://news.ycombinator.com/item?id=23308098 or - using a somewhat melodramatic metaphor - https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...).
It's easy to imagine that the admins should just "get serious about cleaning up this place", until you realize that different users have completely contradictory images of what that would involve, most of which aren't well-defined enough to be doable in the first place. And that's not even the hard problem! The hard problem is that what people experience is the product of a small number of external datapoints and a large number of internal ones.
p.s. I don't think we have a guideline against saying that HN's quality is dropping?