The problem with bards that they have just too low DPS for their "utility".
It was more or less fine without NIN, but with NIN introduced - they just wipe all those little advantages BRD brings into the party and still have much higher dps.
BRD is better on AOE heavy fight... otherwise NIN have better than BRD damage buff, can regen TP too and ballad is rarely useful, so no real "utility" advantage for bard.