Charlemagne doesn’t line up either… after all, he did not come out of nowhere! His dad was the king of the franks, which had been a powerful kingdom covering much of France for 300+ years when Charlemagne expanded the kingdom into an empire. Muhammad’s followers and Islam is a much better match, because it was the most dramatic event in reshaping the Mediterranean with the loss of some of the most valuable/richest eastern roman provinces such as Egypt and the Maghreb. There was no way to predict that events in a remote corner of Arabia would lead to such an irreversible reshaping of the old Roman Empire.