What I always found charming and cheeky is Islam's solution to this problem (if what my devout Muslim friend told me back in high school is true): something alo

What I always found charming and cheeky is Islam's solution to this problem (if what my devout Muslim friend told me back in high school is true): something along the lines of all religious figures and movements are essentially failed/corrupted/lost/etc prophets and attempts at starting the true religion, until Mohamed came around and got it right with Islam. They also say everyone is born Muslim but is lost if they are not brought up in a Muslim family. An opt-out religion, essentially. Very neat and tidy ways to wave away things like Zoroastrianism that otherwise suggest these particular religions are just, as you said, mythology.