So much this!!!! If you're on the last boss and that second (third) LB bar is full, USE THE LIMIT BREAK! It aint gonna fill up more than it's filled up! If that means using it when the boss has 95% HP left, USE IT! Guess what, you'll get at least another 1 bar LB before he's dead, maybe even a 2 bar LB.
LIAR! *beepbeep* ^_^
If they want the run to go faster, stop doing things that result in the run taking longer. Don't put the group in a situation where people start dying.
"If you pull it, you tank it" is a common held stance across the entire MMO genre. It's not unique to FFXIV or WoW or EQ2. If you're not the tank, and you're pulling, you're not being a team player.