Yeah, I haven't been able to find a way to take him down yet either, even with a chain (granted it's Krile's gen1). Under chain, OK BSB, Awakening with EnFire Start + 3 Infusion stacks, AND 2 stacks of imperil, Sora hits for 3500 per hit with the 5 hit fire spellblade against his savage mode. Thinking you'll need either an OSB or the 5* Fire magicite to break it.
Been also attempting Quetz and Behemoth King. Quetz I think I can get since Galuf can use Stone Press to break Savage. Behemoth I feel as if I should be able to beat but only having OK's BSB as a faithga isn't helping things.