Over say having another black mage?

I'm at the point of doing HM Titan farm runs and start Coil but chatter over the FC and some people on the server and some shouts, I always see 'LF DPS Bard' but then I ask them if they already have a bard and they would say yes and I could get my black mage friend in but then they prefer another bard.

I see a lot of "LF Bard" for some dungeons etc but why would most people prefer going for a bard over a black mage in general? Don't black mages do more DPS than bards and have great burst/AoE? So why grab another bard? That would just make the run longer considering you are grabbing another DPS that deals less damage.

Or maybe it's just some sort of community mentality where bards are on a tier of their own and no one knows that black mages can do more.

/boggled