I definitely put too much time into making this post...
Dissidia made the Warrior of Light face Garland twice, Sephiroth, the Emperor, Ultimecia, and Squall all equally without taking damage. Outside of Squall he is the only one cutscene wise to not be outclassed by his opponent in skill. In Dissidia 012 he is last standing hero against a horde of Manikins that killed every other character off. My vote goes to him if counting those games.
A nice point, but Shantotto was the one that Cosmos had as her last line of defense - until Shantotto figured out the whole thing risked affecting her memories and ditched that gig.
Powerful and outsmarting that mess.
Also, every battle lost as her in the game isn't actually her, but a decoy doll she controls remotely, so she doesn't even have to be there to be victorious.