1: Iranians are Aryan (not Arab), which is the same stock as Germans (once we are on the topic of Eisav).
2: Lower sample size does not have anything to do with rates, which are normalized for size (ask Dr. Pepper for more info).
3: The Amish also allow for their children to make a choice AFTER they try being non-Amish. It is actually built into the religion called “Rumspringa”, and its not considered OTD for the Amish. Once you are an Jewish OTD, its much harder to be reaccepted.
4: The best way to keep children on is to marry them young. Many Chassidim (not to generalize) do marry younger than other groups.