Archer has healer LB because SE couldn't be bothered to design a ranged limit break just for archer and bard. It's my strong hope that when musketeer comes out it will get a ranged damage limit break that will also be added to archer. Bard should also really get a seperate limit break that fits both it's support and DPS roles, e.g a limit break that grants a damage buff to the party for a duration.

Healer LB is just there cause SE is lazy. It has a vague fitting on BRD and niche use at endgame but overall it really doesn't fit the class and should eventually be replaced.