First, our military is one of the few to do such studies on effectiveness of its weapons.
You don't read the numerous reports of AK users running out of ammo because the system is essentially "spray and pray".
The opposing forces that deploy the AK do not track how many of their troops are killed because they could not hit the enemy before the enemy picked them off with their superior accuracy.
Yes, the M4 has failures, but in every war, the opposing troops have taken higher losses than our troops have taken. That does not mean we should settle when something superior is available, but it does not mean we should go backwards to an inferior design that has lost to our system in every war.