Usefulness: Bard or Dragoon

[Powercow]

I know we have elemental resistances but I was under the impression our attacks, even for mages, didn't actually do any sort of elemental damage.

Many attacks do elemental damage. The difference is all enemies have the same elemental defense values, so a fire spell will hurt Ifrit just as much as a Thunder spell would. Same with Aero on Garuda. The 10% elemental defense down effect essentially boosts all elemental spells by 10%, which is very nice if you have a black mage in the party and really quite weak if you don't.

The one big part of a bard's utility, and something I never see people mention, is that they can apply a 10% damage dealt debuff to an enemy. This is like, the BIGGEST and MOST USEFUL part of the entire support skillset and nobody ever freaking talks about it. It's seriously better than the mana song, the tp song, and the elemental song combined in terms of its overall usefulness.