They've only ever been DPS, same as Samurai, or a Ninja, or to a degree a WHM or DRK.
It's a matter of how dependent their rDPS contribution is.
A Samurai will have the same personal contribution regardless of raid size, although slightly enhanced if the lone source of Slashing debuff among other slashing classes.
A Ninja will require more people to have the same pay-off.
A Red Mage will require more mana- and GCD-intensive play from its healers in order to pay off, by way of Verraise.
Summoners, even omitting raise, require other sources of magic damage and at least one ally to pay off, by way of Contagion and Devotion.
If you've thought about Bards as "support" DPS before, hopefully you're already aware of their dependencies.