Tank's and Bard's LB are situationally useful too.

The three bar Bard LB has saved our asses more than once when the healers died, so we could finish the fight without wiping.

Tank LB has saved our butt in Garuda when we were doing the story quest and in a couple of different dungeons.

Melee DPS definitely gets to use the LB more often, that doesn't mean the other ones are not useful.