Why do people always feel the need to reduce everything into oversimplified, binary classifications of X is better than Y? Bards and Black Mages are different. Bards do amazing DPS and their ability to DPS on the run is indeed superior to Black Mages. Can a Bard sleep a ton of mobs that are about to swallow you for dessert? Can a Bard throw that oh-so-important l3 LB on Ifrit's Nails? Don't be so obsessed with being the best in every category, but rather with being able to maximize your potential in the specific role your class was designed to play.