I'm not sure why people are treating lore as if it would be an issue. "Something something, lost lore of Allag (because it's always Allag), they figured out how to make a pact with a Voidsent or something and now you too can use their magic". I mean, you can make up a thousand variations on the idea of "something lost to the ages now is discovered which changes our views on everything". They even did that in Shadowbringers with Astral/Umbral being Dark/Light instead of the opposite.