To be fair, I don't think there was ever any doubt that survivors of Amdapor and Mhach would've been responsible for Red Magic and the Red Mage job.

But you have to admit the old theory that floated around for a while had merit. Dissidents/Survivors of the War of the Magi left Eorzea to escape the Witch Hunts and founded Sharlayan, pooling their arts to create Red Magic, and training Red Mages to protect their new haven. Having learned from the past, they dedicated the pursuits of their nation to learning and chronicling history.

What we have now follows the start of that theory, but instead of doing the logical thing and fleeing the witch hunts, as well as learning from history, it seems some remnants of Mhach and Amdapor just decided to tough it out instead, and go down the same path.