Yeah, MMM was cool and weird but the rewards were never good enough to make people do it. WotG overall was a weird ode to midgame (xp spots people never used), and MMM was particularly weird because you had to have pretty beefy characters to do it for mostly sidegrade rewards (don't @ me koggle blus).
Monstrosity (not just Buburimu grinding, but visiting different zones and playing different monsters) is also really enjoyable IMO. It was _such_ a good idea to functionally add like a hundred unique jobs to the game at the low low cost of ~0 additional coding. Unfortunately, they destaffed it, pushed out the releasable stuff that was in the pipeline, and that's how we got a shitty PvM system in the final release that gave an extra 50 set points and broke balance. Subsequent updates powered up low level black magic and made the problem worse, which is why "optimal" monstrosity these days is killing stuff in Bubu over and over.
Pankration was cool, but it needed to be more interactive and they more or less abandoned it shortly after release.
There are some interesting quest lines in FFXI, Return to the Depths, the one that involves going to Jugner a lot (don't remember the name and not sure how to avoid spoiling it), etc. but honestly I find the quality of this game's story and quest a bit overstated by the people who still play the game. It's rare that they're willing to grapple with weighty issues, which means that plotlines top out at surprising and I hardly remember most of them.