Without adding a new race, Sylphs are pretty much all that are left to represent lightning. Goblins are fire, Qiqirn are earth, Moogles already summoned Moggle Mog... Now, sure, the Sylphs said that the primals darken hearts and should never be called and they'd never stoop to that - but that was before Bahamut showed up and just completely wrecked them. I'd say at least a fraction of them would fall from grace and demand revenge...

Et voila - Ramuh