Many people still consider Taken King and (for some reason) Rise of Iron to be the pinnacles of the series and they only had the one raid each. And while we never had a three raid/dungeon year like you said, base D2 had a raid plus two raid lairs, and even I quit for a while back then. Lightfall had a new and reprised raid each plus two dungeons, and that is the only other time in this game where I stopped playing for months. Pretty sure I’m not the only one, people were very vocal about how dogass those releases/expansions were. Hell, the only period of D1 to feature two raids was year one, and people were VERY vocal about how dogass that was. Then we only got one raid a year and people started loving it! Given all that, I don’t think “number of raids/dungeons” is a good indicator of how good the game is over a given period.