In theory, it sounds nice.
But...it's basically adding a new job gauge to every single job.
How do you make it feel good compared to the job gauges? Just by making it a flashy nuke?

And it also impacts other things for expert players:
Do you have to line it up with the raid buffs?
Does it weave in nicely in the rotation, or does it delay your whole rotation if you use it?

I think the main changes that would be cool are
1) LB1/2 of healers and tanks should deal damage, so that they could actually have a reason to press the button in dungeons.
2) ranged/caster LB3 could hit stronger if it only hits one target, so that we could see them being used more frequently than just when there are annoying adds.
3) tank LB3 to be required more often, or updated to an overall stat buff instead of just increasing defense...since the game is all about DPSing...It's usage is a bit too situational and scripted at the moment.
4) RDM LB3 visual effect should be toned down a bit