All the support classes have an interrupt and a 10% less damage cooldown as base.
Machinists don't have anything else support wise so they should do the most damage.
Bards get songs that increase healing and DH and should do the middle amount of damage.
Dancers have the most buffs between defilement,standard and technical finish and should do the least amount of damage.
Problem now is dancers do too little damage and our rdps doesn't make up for that. If dancers get a small potency buff then bards should probably also get a small bump to keep them over dancers.
BRDs are already far enough ahead of DNC in personnal, a bump to DNC personnal wouldn't require any other change. When factoring Rdps, the classes are fairly close(DNC is 1300-1500DPS rDPS on top of their own). Even the other classes are kinda close, including Ninja(although it requires way too much effort to optimize). That does put selfish classes like MCH and SAM in a really bad spot though since they're all fairly close to DRG/MNK, and while MCH at least has its own advantages(ranged, no cast times, very high on demand burst by stacking heat windows even outside of wildfire) but SAM kinda sucks atm when you can get a MNK doing roughly the same dmg but with Mantra and Brotherhood, and DRG doing slightly less but with much better buffs.
If I had to guess:
Tanks: WAR and DRK slight damage buffs. Dark Mind mitigate 5% phys or boosted somehow, maybe finally Living Dead QoL buffs like only need to heal 50% or increased healing received.
Healers: AST medium/large personnal dmg buffs, WHM slight personnal dmg nerfs, SCH maybe getting a random oGCD to weave to appease the masses but unlikely to be tied to Aetherflow, not ED cause SMN have that, damage values lowered slightly to accomodate(or the damage buff will put them in the new projected values of the other 2 healer changes so no need for nerfs)
Melee DPS: Ninja bit of personnal DPS up, maybe some QoL changes(Bunshin to 2mins instead of weird cooldown), SAM relatively large personnal DPS boost(like 1k) via either new trait buff(the jinpu shinten one) or just potency on midare or whatever, DRG medium nerfs, probably jump potency or something like that.
Ranged DPS: DNC slight personnal buffs, bit of potency here and there or preferably tweaks on the % proc of Esprit(which should be displayed in tooltips), MCH small damage buffs(500ish).
Casters: RDM mp cost reduction(they're mp negative even with lucid spam, which is terrible design since them dying can lead to them actually not being able to play the rest of the fight), Reprise buffs, slight potency buff somewhere to even out SMN playfield, SMN honestly no idea their rotation is some huge fuckery and would need a pretty indepth rework to unfuck. Maybe both should get potency buffs though, the rez penalty is pretty hard atm and with mp management the way it is, it's not like they can chain rez like they could in some groups in SB with Refresh.