was i wrong to use limit breaker?

[whiskeybravo]

Disagree strongly with your general rule.

Caster LB is superior in most dungeons (to clarify, in case you are confused, it's better to do 20000 damage to a pack of mobs than 5000 damage to a boss in terms of speeding up the run). Melee is superior on single target encounters, such as trials and some raids.

Appropriate LB is appropriate. If multiple enemies then caster, if single target then melee. Melee usually gets priority but it depends on the situation.