it's understood that the history, as presented, doesn't really add up - it's not consistent with itself. and, these texts took some time to actually write and compile.
what is less controversial is that the balance of evidence suggests that islam, as we understand it, was an invention of the ruling class after the conquest, rather than something that developed spontaneously, before it.
the entire society collapsed in the 7th century, and islam was the consequence rather than the cause.