You know maybe not all the Primals are Elezen but there is some new room for speculations according to recent lore from 2.4 (Binding Coils of Bahamut) if my belief is somehow true the Elezen are somehow superior with connection to the Gods and the Echo then other mortal and the power bore from Louisoix and Alisae in the binding Coils of Bahamut are something from a long line of powerful Allagan sorcerers whom may have had a connection to the Twelve themselves. melted down Elezen are superior to other species in terms of connections to the planet's Aether therefore Elezen would likely be the most likely catalysts for creating a Primal most notably Shiva, Ramuh, and Garuda are in fact the most obviously likely to be Elezen before they were even Primals whatever they did that got them turned into Eikons most likely through interacting with the Twelve they became the Primals that we know now.