Jehovah's Witnesses: How do you reconcile the rapid growth of Islam with your interpretation of Rev 16:12?

Islam isn't growing as fast as Muslims like to make others believe. Almost all of the growth is due to high birth rates. There are lots of people leaving Islam all the time which is something they never talk about. A lot of people are also afraid to say they don't believe in Islam anymore so it's actually impossible to know how many "Muslims" are actually Atheists or something else in secret.