I want the job system to support diversity of playstyles. I think that's impossible so long as you have party buffs , so I would first remove ALL party buffs (except Bard, elaboration below).

Now that we can have different damage profiles, it's possible to (re)introduce missing job playstyles such as:
- DoT upkeep
- random procs that change the core rotation (not just damage oGCDs)
- ramp-up damage (gradually build and maintain self-buffs)
- flat damage with no burst
- burst windows at different times (30s, 60s, 120s, 180s, etc instead of just 120s)

As for more specific changes:
- MNK: gradually build up greased lightning, which can get your GCD as fast as 1s. No oGCDs at all, they are all turned into GCDs instead. Even Feint and Arm's Length are replaced with MNK-exclusive GCD cooldowns
- BRD: you can still have the songs, just not the 120s party buffs like Battle Voice and Radiant Finale. Each song should change your core rotation more than they do now.
- MCH: walking casts
- DNC: no party buff. You still pick a partner and buff them, but your buff timing can be varied based on their rotation. You would achieve this by building a gauge which is spent on each step in Technical Finish. e.g. you could dance 2 steps every 60s for a 10% partner buff, or 4 steps every 120s for a 20% partner buff. In this way, you are rewarded for understanding your partner's rotation and matching your timing to them. Just like real dancing!
- BLM: revert most changes back to Endwalker, with the exception of
---- No waiting for mana ticks, MP is restored per-GCD used in Ice (any GCD, not just B4)
---- 2 stacks of 30s Leylines on a 180s cooldown. No way to Retrace. You are rewarded for the fight knowledge of when to safely place them.
---- Remove Amplifier and reduce the max number of Polyglot stacks. Flattish damage profile, not bursty.
- RDM: white/black stance to choose between Verraise for prog and more damage for the kill, long cooldown to change stance. Vercure builds (or spends?) white mana.
- SMN: 12+ egis unlocked via MSQ progress. You summon six of them before you can summon the first one again. Yes there will be a meta choice of six but we can make some of them stronger in AoE, twin-target or CC situations so they'll see some use in dungeons, side content and the rare add phase.
- All healers: fewer oGCD heals
- SCH: 5 DoTs & stance dancing
- SGE: a DPS rotation that is at least as complex as current Warrior
- DRK: a rotation that includes spending your HP to deal damage, then stealing it back from the enemy. If you time it wrong around a raidwide/buster, you will die.
- WAR: No self-healing, that's DRK's deal.