Therefor I suggest using a specific LB in the form of a skill that is equal to all classes. An LB skill that you can activate from the start of the duty and that cannot be activated again in the same dungeon once used (doesn't need to build up).
An enhancement LB wich adds to the strength of all your skills/spells (including the effects and the shared LB if its still unused) for lets say 15 seconds.
But then they would need to re-balance ALL content to account for this new buff. And then, once they do that, the net result will be the same difficulty as now--so that begs the question: what are we gaining by adding this? Also what dungeon is so difficult that this would even be necessary? You can already clear every dungeon WITHOUT Limit Break, so the Limit Break we have now already is just something to finish the boss off at 5-10% to lower the time it takes to clear.