And also, "something like leather armor" is actually not so light & unencumbering after all. Especially in desert conditions, where metal armor may even be better (after all, it doesn't become drenched with sweat, turning heavier in the process)! As for various bits & pieces included under robes - well, under current rules, robes DO provide some protection, aren't they?
As for being undisciplined, you should note that the same Koran iirc states that "you shouldn't run back & forth but keep you place in ranks with you comrades" or something along these lines... it actually reminds me of military textbooks very much, providing treatises on discipline, marching order, feeding of troops & so forth...
It certainly wasn't always listened to, but discipline is currently thought by many to be among the main reasons which allowed Arabs to beat up better armed contemporary Byzantine & Sassanid (Persian) troops (though Mongols were surely much better)...
And - what DO you think about names for MA/LA proposed?