Raise your hand if you've ever died because you used a limit break.

Considering the frequency of things you need to react to during battle, the LB attack animations can feel like a mini movie in length, during which time you are unable to control your character but still receive damage. In the time it takes to use a melee LB on the frosty dragon add, Midgardsormr has used 2 different aoe patterns that you were unable to dodge.

Would it really be game-breaking if we were invulnerable during the time we are unable to move? Especially because it would only apply to the user of the LB and not the whole party. I think LBs should only be a good thing and not have any down side like being unsafe to use in certain battles.