Cons: Stagger: Wound Stagger: Wound Stagger: Wound weak to fire ridiculously expensive to raise ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ In the end, I'd give the nod to Proto. The 6 ATB only really helps Narasimha with doubling up on Area Sweep (which is better than Blitz) and against launched enemies. Per ATB refresh they both get about 8 attacks. If you couldnt tell, Stagger: wound is a huge hinderance to Narasimha. The RL's on Proto arent really anything amazing. They could be infused into Narasimha if you so desired. Due to not having Stagger: Wound and having Bloodthirsty, Proto will hit harder except against non-staggered physically resistant enemies.
6 ATB Higher strength than either Proto or Narasimha No Stagger: Wound Bloodthirsty Area Sweep
It's the best Behemoth COM.
Also, Proto's Bloodthirsty can actually be a hindrance due to how it will override Armor Breaker (and result in less damage) as soon as you inflict any Wound damage at all on the target. You can get around this by stopping Proto at Level 33, right before it learns Bloodthirsty, at the expense of Bravery Feeder and a few stat points. This results in an inferior Proto only against Nabaat (who's immune to Wound damage and thus will never invoke Bloodthirsty) and any fight in which you'd use Proto and need Bravery Feeder for some reason... but it still wouldn't be worth giving up Armor Breaker. Maybe against Yomi. But you shouldn't use Proto against Yomi.