Islam just means " submission to GOD".
Islam existed since mankind existed.
What you seem to be talking about is " traditional islam" the religion practised today!
Well of course that did not exist before Muhammed, like Judaism did not exist before Moses and Christianity did not exist before Jesus.
You will also notice that there are a lot of man made stuff in all these religions.
By the way you have not answered in this thread that you have opened, are you still interested?
Or are you just leaving others to discuss your " idea"?