Limit Breaks are [extra damage]. It's never a DPS loss because the overall group's DPS skyrockets when used, as it does over 100k+ damage. Since LBs are extra and allow wiggle room for finishing faster or avoiding a wipe, the cost is their limited use and the time it takes to cast it. Similar to benediction/hallowed ground. You're doing 100k damage instantly or raising 7 people to full HP with no weakness, you're gonna have to be out of action for 5 seconds. Deal with it.