Playing for fun? You mention H3, but once you hit 50 it was kind of the same thing however you didn’t know when any new content was coming. We got events scheduled, and a new mode on Tuesday I believe.
once you got 50, you would then be grinding for 5 star general and trust me 50 was not easy, took people months to get particularly at the start of the game, i got top rank in 3 days
I know all about Halo 3 and grinding. My entire childhood was leveling alt accounts with friends lol. Hitting 50 was quite easy if you had a crew coming with you from Halo 2.