Same here. The historical aspects of Athas should be beyond the scope of most PCs. Because of the way Athas was originally created as a kind of “historically neutral” setting, you could have literally any backstory for Athas. I’ve seen a ton of alternative historical backstories, from those involving the gods to the illithid empire.
And what is to say that Rajaat is the bad guy. Perhaps Rajaat was bringing peace and prosperity to the world, while his students perverted his preserving teachings into defiling.