One of HN's origin stories is that pg finally got around to writing it when Steve and Alexis stopped accepting his feature requests.

Oh that's interesting. I remember being hooked to reddit when it launched. And then after a while it started slipping and was happy to find HN (quite possibly through reddit or maybe pg essays) which was a bit like the original reddit, but much better.

Precisely, and that was no accident, since the idea for both sites came from pg. Of course he knew it was in Reddit's interest to grow, but when it lost the property of being interesting for him personally to read, he created HN, a smaller sibling, and kept it that way by design.

It's also one of the reasons I want to write something like HN.

You should. HN can't be all things, so if you'd rather have something else, create it and make a community with others who share your preferences. Several have spun off from HN over the years, much as HN did from Reddit.

There is room for a lot more internet communities. Plenty of permutations haven't been tried yet, or were tried and failed for extraneous reasons.