No the fastest-growing religion is Buddhism...because people around the world are becoming Buddhist on their own without any pressure or death threats !
Islam is also growing fast...because muslims around the world are having more and more kids and also some are converted due to pressure and death threats which is the norm ever since Islam was founded.
Only about 3000 Kalash people (Greek descendants of Alexander the Great's soldiers) in Pak-occupied Kashmir are left as more and more every year are being forced to adopt Islam.
Whatever good stuff in Islam is being negated by terrorism. Eventually (may be 1000 years from now) people of the world will reject and defeat Islam and terrorism.
That's what happens to all dictators...in the short term, they bask in glory but eventually they fall hard and get finished !!