There's no way that LB1 does LESS damage than normal RDM AoE. It's a good possibility that you either aimed the marker incorrectly, or the mobs were moved outside it's radius before it went off (both of which would cause it to miss the targets and do no damage). Caster LB1 should at least knock about 1/4th to 1/2 of most trash mobs HP. If it doesn't, it's probably just a mob that has lots of HP (and there are a few, especially in later duties).