Let me thing...I think my level is/was somewhere in 70s to 80s and there is a way to save yourself from that attack which drams your HP/MP.
First, equip Second Chance. It means you'll always survive it with at least one HP, meaning you can use a potion to heal. There's also an ability you can use which removes the finisher from your combo, meaning you can just spam the attack button and wail on him. As soon as you start hitting, he has no recovery until your MP gauge recharges and brings back your finisher.
I'd also recommend Combo Breaker; it open his guard and stuns him for a moment.