Hmm. . .with the difference that none of the Eikons we've seen bear much resemblance to any known historical figures, with the exceptions of Louisoix and possibly Bahamut. Even Shiva, known to be based on an Elezen woman of the last millennium and inhabiting the body of an Elezen still alive, becomes something of a caricature. Odin, who may once have been a man, is now the Eikon Zantetsuken, which tempers any who wield it. Leviathan may have been based on a sea serpent (indeed, sea serpents are often confused for him), but there are enough differences to distinguish the two.

Basically, what I'm getting at is that even if someone were to summon the Twelve, they'd be far, far removed from even the appearance of the mortals their myths may have been based on. Whereas A-Towa-Cant seems to be himself upon his manifestation.