Yes, they can stack. But for 4-man content, bards are still one of the better damage dealers.

Swiftsong gets the group to the next pull faster. Plus they inherently have high, controllable burst dps due to cooldowns being available for every single pull.

I guess you probably should hope for a black mage or summoner as the second dps. Just not monks. Monks may be overpowered for raid content, but they are less than ideal in 4-mans.