I like the idea that Ramuh, Garuda and friends are the 'gods' of the beastmen in the same way that the Twelve are the 'gods' of the Eorzean people. Presumably this presupposes that - as Moose said - 'something' exists on another plane - the aetherial plane? - that is the essence of each of them. Summoning one of these essences creates a physical form that is what we call a Primal. The idea that gods are created by belief and prayer is one I've come across a few times in my reading on myth, religion and psychology (though whether those writers think that these gods can claim an actual reality in the way it seems they can in Hydaelyn is another question XD).

Presumably Zodiark and Hydaelyn herself are a notch up the ladder from the Twelve? And King Mog & Shiva a step down - maybe on the way to god-hood if the belief and prayer is strong enough, lasts long enough? What about Midgardsormr? His relationship to Hydaelyn fascinates me; I feel as though he talks to her almost as though they're equals. And Odin and Bahamut are Elder Primals just because of their longevity?
What happens to these 'gods' if belief and prayer in them diminishes?