Bring difficulty back to job rotations, not just boss mechanics.

[Azurarok]

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Marketing for Savage and Ultimate gives it an enormous level of prestige that other difficult achievements simply don't garner.

Ah right, the reward of having cleared an Ultimate is definitely a lot more obvious. There being a time where YoshiP personally congratulated Ultimate world firsts also must've boosted awareness tenfold too (Then TOP had that 3rd party tool fiasco).

I guess there's also just the spectacle of it for those watching streamers play. 20-ish floors of similar looking areas for 100 or 200 floors isn't exactly exciting to watch unless you know how it can be yourself.

That might also be why they're focusing less on rpg-like elements and job complexity, it's easier for any non-player to see and get a better gist of what's going on. Think FFXVI was also that, boss fights that are absolute spectacles to watch, but not much gameplay depth to make it particularly fun to control.