Make a small change that would break a class completely.

[Kassiekane]

Ninja = Kassatsu's cooldown is reduced to 40 seconds.
Warrior = They can now cross-class Invigorate.
Monk = Fists of Fire's bonus is increased from 5% to 15%.
White Mage = Presence of Mind will temporarily nullify MP requirements for all spells.
Scholar = Galvanize can stack.
Summoner = Bane is no longer limited to 3 targets.
Dragoon = Can cross-class Berserk
Black Mage = Apocastasis will affect multiple party members, including the caster.

[Kuwagami]

Summoner = Bane is no longer limited to 3 targets

you mean, like it was before the 2.1 (or was it 2.2 ?) nerf ?

here my list :

BLM : no monster is immune anymore to sleep
BRD : swiftsong in battle (I would have said give us the original RoD back, but now WARs have it, so.. yeah...)
WAR : overpower is now MP-based (of course, their MP pool remains super low)
PLD : stances are no longer on GCD and do not break combo anymore (second one should be QoL thing. meh)
SCH : a critical embrace shields the target
MNK : GL has a 20 seconds duration
DRG : ellusive jumps actually counts you out of the AoEs when you're out and not when you land (oh maybe that should be an other QoL thingie instead ? ;D )
WHM : shroud of saints nullifies hate generation for its duration on top of the current effects

The only "nerf" about Bane was the skill description, not the skill itself. Only the description got changed.

is that so ? my ACN was lv15~ish at that time so I always thought it was a nerf. thanks for the enlightenment

[Felis]

you mean, like it was before the 2.1 (or was it 2.2 ?) nerf ?

The only "nerf" about Bane was the skill description, not the skill itself. Only the description got changed.