Honestly I would've used it on that first boss as MCH.
I would've used it as MCH on final boss if the melee didn't use it right as LB2 had ticked off (maybe not RIGHT as but yanno..don't wait)

I'm tired of people waiting to use it as a finishing move. Use it or lose it. You did fine, they were probably going to wait till the last ten percent to use it (and that's a waste).