I think the only way of balance the jobs.

Example

Red Mage, Corsair and BRD.

RDM. Attack/RA. Attack 30%. Accuracy/Ra.Accuracy 20%. MA acc +15% / MA Att + 20%. Can use 1 Buff and One Debuff.

Corsair. 3 Dices by default Instead of 2. Unlocking M/E/A Any "Lv75" Legendary weapon, Unlocks 4 Dices and the ability of Stack same Dice x2. Example X2 chaos Roll, X2 hunter Roll etc.

Bard. 3 Songs Default Instead of 2 and Song duration 90 Seconds More. Unlocking any R/M/E/A lv75 unlocks 4 Songs and duration + 90 Seconds + Potency of All Buffs +10%.

To avoid People Exploit the System. Max Amount of Dices per party 4, Max Amount of Songs per party 4, Max Amount of RDM Buff/Debuff 1/1, Max amount Geo buff/debuff 1/1.

Put Something like this in the Test server 1 Month. Then ask for Feedback to the Playerbase, after all the Feedback received here add the Buff and Keep testing to see if the situation changed. If this work Nexth patch Two-Handers, etc.

Like other people said here. The difference between some jobs its brutal.