The Eternal September comment rings true. There was a staggering change from 2006-2008, and a gradually decelerating decline ever since. Site policy changes are not necessarily the primary factor. As an audience gets orders of magnitudes larger, it grows diluted and less cohesive. That said, I fully agree with DanielBMarkham's comments from the election thread (despite having been in political agreement with the majority myself).
PG has made truly non-PC comments here and in essays. His writing isn't that of a populist or a cultural conservative by any means, but is also clearly out of tune with the bay area echo chamber. There is a wide space between supporting Trump and not fitting in in SV! Broadly, the political topics pg seems to write about have been an opposition to political correctness, favoring equality of opportunity, and a belief that individuals creating wealth help the world rather than harm it. Some of these positions were either left leaning or had broad popular support 20 years ago, but most would now be considered right or centrist. This, coupled with his previous willingness to voice deeply sensitive but true observations, may have lead to his retirement (e.g. "founders with strong foreign accents have less startup success"). Things may have changed after Valleywag took aim at him, however.
The only "battle" being waged from this side is
1) for the pursuit of truth
2) for the freedom, happiness and well-being of every human to the greatest degree possible
Trying to accumulate karma leads to ever stronger filter bubbles. Consequently, karma is a resource best spent on ideas that are both possibly true and deeply unpopular. Given the willingness to dissent and the apparent alignment of goals with HN's stated guidelines, these and future comments may possibly serve as a useful canary in a coal mine.