Well Primals drain aether form Hydealyn (the planet), We get out power form...Hydealyn (the crystal)
As for the Dark Warriors being primals, we do know that primals are not really the gods they are based off of, but figments of imagination in their image, made flesh.
Then again we don't know all the differences between a Primal and an Eikon other than age and the fact that they can apparently be substantiated without followers (and even that's a thorny issue since Zantetsuken tempers its wield to become the next Odin, while Bahamut had a graveyards of followers inside Dalamud, and yes it might as well been a graveyard, if not a personal hell, for the treatment of the Meracydians, but that's another topic)
