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Except the Odin and Alexander are also both Prime :p

But I get what you're saying. Personal, I'd want the original Bahamut and for him be a Non-Elemental Avatar. They have the Whale model, too bad...

They've already made it very clear there are other dimensions with Abyssea, Voidwalk, and Escha. Adding Phoenix should be easy, as it already has a model in the game. Personally I'd like her to be...