Honestly i think the heal is fine, I feel a single target attack doesn't really fit a bard (not only that but we already hit like trucks). However that doesn't mean i think the heal is the best option.

I think a cool limit break would be a song that provides buffs to damage, defense, mana regen maybe and so on....maybe depending on your class you get a specific buff or maybe everyone would get like a 10% increase to everything for x seconds.

Again the heal is fine, but if the do change the LB it needs to be to something like this not something that makes me shoot a giant laser at the enemy (as cool as that would be)