It's possible that someone who thinks that Hacker News was "a bit better earlier on" favours that, especially as (as pointed out elsewhere in this very discussion) those are noticeably lacking from the page at hand. So let's see what the answer to my question is.
Dicussion on Hacker News is not qualitatively better than on any number of well moderated technical subreddits or niche trade forums, and most of the articles posted here are cross-posted from Reddit and other sites. The only real differentiating factor is that Hacker News aggressively downvotes humor and polices for tone.
Every now and then threads pop up asking about alternative HN-like forums, here are some:
However, HN is also effectively a monopoly. There's really nowhere else to go to find the same type of discussions.