After reading Aatrox' lore again, I've thought about something. Before the Institute and the League were formed, Summoners were the leaders of armies and figureheads of their political organizations, and were the ones that brought down the heavy magical assault.
It seems pretty likely that the Magelords would be the original all-powerful Summoners. Their names support that, as well. It also seems like they weren't the "good guys". Maybe the Protectorate was defending the world from their magic-fueled ambition and thirst for power?