It seems limit break might have been a poor choice of ward because reading them it seems like it has nothing to do with the party gauge. The problem with massive cooldowns is that they need to be on large cooldowns and you've picked up on that. The problem is when they are on cooldown. With the limit break you get usually one massive damage spell dependant on who casts it for the whole party each fight. With a personal massive cooldown you have 8 other people with one and then encounter designers have to design around 8 people using their massive cooldown. If they don't then the fight becomes trivial. If you still have your massive attack on cooldown then the encounter is impossible to beat without it. If you are doing coil for instance do you wait 15 minutes for the cooldowns. Seems a waste.