It's true that "HN is turning into Reddit" is classed as an Eternal September-style complaint in my mind, and I think also in the minds of most people who make those comments. You're the first person I've heard suggest that it might be a cyclical ebb and flow. The comments we're talking about never have anything that subtle to say.

I think you're underestimating how common this trope is, and how mechanical and vacuous it is. It has been that way for well over 10 years—since before HN was even called "Hacker News" in fact. It got so tedious that pg added that site guideline a decade ago.