Interesting question... Hmmm...

1. MSQ
2. Crafting & Fishing
3. Baldesion Arsenal (I just wish the participation wasn't carried by Discord groups)
4. 1.0 Diadem.
5. Hunts.

I would say achievement hunting but that is far too generic and all-encompassing. the original Diadem just had something to it which I liked, probably in that it was exploratory for exploratory sake, rather than being a vehicle for relics and/or leveling. It had the advantage that you weren't really aiming for a significant grind and still had the beauty in that you had Trials of Matron and Trials of Fury, and the emergency mission was just... Fantastic. Bozja was fun, I guess... But what it has become and what it is a vehicle for has just made the core of it feel so devoid of substance. FATEs go down in seconds. Sure, you have the Critical Engagements, but each of these was on a, what? a 90-minute respawn timer.