Actually - if you go through the current lore. The current primals that we have fought are considered "corrupted" primals. Something about the process the beastmen use to summon them seems to corrupt their essential essence. As such you could make a strong argument that all of the current primals represent a corrupted aetheric entity manifestation. Because this aetheric summoning proccess can apply to ANY entity there is no limit to these corrupted fights. That said i would LOVE to see some story around interactions with uncorrupted manifestations of the primals.