Realization: Is the WoL a primal?!

[Settiesama]

I had this theory way back that the WoL only appeared during the Umbral Eras because people across the world would hope and pray for a WoL to return during the dark times, and so the Aether that flowed through the planet would respond with one.

Or.. Hydaelyn decides to choose someone to become the Warrior of Light (might even choose an unborn baby) during said times. Which is how it's explained in the game.