The challenge is to have the Middle East except for Persia and Arabia become majority Gnostic by 600 while still having Europe and North Africa become majority Nicene Christian as in IOTL. Would that necessarily require the overthrow of Roman or later Byzantine authority? Or could some sort of compromise be made with Gnostics in order to maintain control over the Middle East? Also what would be the effects on Islam if the Middle East was Gnostic at the time of the Arab conquests? Or would Islam be butterflied away?