question on limit break

[Nutz]

Completely dependent on the average iLVL of the weapons in the group. Who uses the LB has no impact on the damage, and also, no buffs or anything impact the damage done.

This is accurate. As such, you'd want the weakest melee or caster DPS to use the limit break, depending on which type you want to use. Sometimes it's preferable for a MNK not to use the LB because it can cause greased lightning to fall off if their skill speed is too low (potentially wasting more DPS than if a better geared DRG or NIN used the LB, for example).