The strategy I used for the final boss of this dungeon is to just spam hits but, not use any aoe. Treat the fight like you are fighting Belloq in Twin Giants. There an equalize cheat which caps damage at 3,000. Attack the White Tiger boss first until he dies. Then attack the Power Draconian with spam hits as well until he dies. Do not use any aoe hits so no storm lord, tempest, dragoon amulets, scald or any spell that targets all enemies.
A strategy that might work is the nightbringer change bubble strategy that was frequently used on Fellspawn. Ideally best strategy have everyone spam and have like one healer as back up.
