They were still Moslems. One would need to treat Islam the same way the Brits treated the Thuggee. Note: I am not advocating for this, merely pointing out how it could be done.
The Turks were and still are pretty decent fighters in that part of the world. I think Arab culture is sort of special. Islam+Arab culture = hot mess in close combat. The Ottoman Empire had a pretty good run and I would hesitate to attribute its fall to Islam or Turk culture.
Another example of effective muslims in combat are the Chechens, but they are more hillbilly badass like highland scots and their descendants. Not sure if they could work it in a large organized military.
But, yeah, not a lot of real standouts in the Muslim world. Without a caliph and a weak opponent, they are not too impressive.