The answer is in the skill cap:

Bard is "easy mode" and can achieve near maximum potential with a simple rotation while on the run. Dodge and proper movement during any fight in the game has little effect on BRD's dmg.

where as

Black Mage, Monk and Dragoon have a much higher skill cap... Proper rotations are much more difficult to master, positioning to dodge and move properly can interrupt your rotations and throw them off.

Bard was always meant to be a utility job... why do you think they were given songs and a healer limit break?

As the other DPS jobs become more practiced you will quickly find them taking over the DPS king positions.