I've read a lot about that, my take on it is that there are two definitions of Arabs. Bedouins(in the past they were just called Arabs, I think it's the same in the Qu'ran), these guys live in the desert and are good fighters, Israel uses them in their army and they also did the brunt of the fighting when Lawrence of Arabia recruited arabs against the Ottoman empire. Libya and Egypt also created their early armies out of bedouins, they are good fighters but not very sophisticated, they're mostly illiterate, you can't train fighter pilots or even good tank drivers out of them easily.
Although Muhammad was a city dweller I believe, most arabs at his time were at least partly bedouin(even mecca or medina citizens had to travel by horse or camel and live out in the desert to conduct trade), and these were the guys that conquered the Middle East. Good fighters in general.
The other kind of Arab, the modern kind, are the sedentary middle eastern people that happen to speak Arabic because they were conquered but come from many different origins like Egyptians, Syrians, Iraqis and so on. I personally find that self identification rather weird, even black guys in the Sudan call themselves Arab(and oppress other blacks who don't identify as Arab), I feel it's like if Mexicans called themselves spaniards or Jamaicans called themselves English.
These guys were for the most part never known for being warriors.
During the middle ages they relied on Turkic or European slave warriors, guys like Saladin(kurdish IIRC) is revered as a kind of early arab hero but his army consisted mostly of Seljuk turks. The Mamelukes were also mostly turkic*.
*You probably know that but for these that don't know, Turkic is not the same as Turkish, it includes people that speak turkic languages, not modern Turkey citizens only.
