Bards certainly don't have the best dps.

That being said, every raid has a bard for their songs.

Every raid also has a spot for BLM certainly. They are very good AoE dps, great burst during astral phase, completely resource independent so they will not run out of TP (or mana, for summoners) on extremely long fights, and solid single target dps as well.

I haven't heard of anyone turning down BLMs.