Honestly, I can't find a real problem. It'll shake up early approaches a little bit, then from there you'll have an expected use case, like normal, but the ability to create more areas of use with good planning and teamwork.

My one concern might be that it encourages excess damage intake, but SE generally puts enough discouragement through Damage Downs there, but otherwise, I don't see anything inherently faulty about this approach compared to what we have. Old Ifrit interruptions basically work on this premise, and seeing a full LB gauge come from your own action never felt bad.

I'd wager you can extend this to other tank-typical responsibilities such as short term crowd control, interruption, and debuffing. Turning the invuln/super-state into the tangible reward works for me, though I obviously don't speak for anyone but myself.