Military genius is as much about getting a technological edge; the stirrup, the long bow, Damascus steel, etc. Arabs ran out of superior technological cultures to plunder.
Sorry, but I don’t buy it. The Mongols and Turks and Kurds (Saladin) and Mamelukes had no technology not available to Arabs, but they conquered all over the place from 900 to 1800. The Arabs just didn’t.
Arabs were not a conquering people before Mohammed, and they haven’t been since 900. They had a brief moment in the sun and then lapsed back lassitude.