> HN posters tend to be overly critical, often tripping over themselves to demonstrate

That's the helpful part though, as one of the only communities that is overly critical instead of too much on the other end of the spectrum like every other community. Criticism helps you refine and sometimes even see new perspectives, and the other chaff and useless comments you can just ignore, doesn't really matter, as your experience shows as well. Ultimately I think you get back what you put into the HN-machine.

I do agree LLMs water down human writings to a extreme degree and people should just wholesale avoid them except for very surface-level copy-editing fixes, like spelling mistakes. Don't ask for their feedback how something feels or if it's "dumb" or whatever, use your own intuition.