2016-era HN had its share of negativism, but it also had a lot less people - the light green from those charts is misleading.
I do think as a metric for total reach, a static cutoff actually works reasonably well. I think some form of square root normalization over total users is probably the best balance.
Do you have any insights into the Clawd spam ravaging /new and /show?
I'm in there, being part of a (down) "voting ring" (not coordinated)
I was planning on doing this yearly but the Clawd excitement is definitely worth diving into.