I accept the InRange and Forgotten Weapons mud tests as valid (they also did dust/grit tests as well, where the AK did better than the AR, IIRC), but I wonder whether the locale (Arizona) may be skewing the tests a bit. Their "sloppy mud" often has so many small pebbles in it that it resembles wet concrete. That's what makes their tested rifles fail - small rocks in the trigger assembly or in the bolt lug recesses of the receiver or trunnion.
For some recent "practical accuracy" comparison of the two platforms (and many others), an excellent YT channel is 9-Hole Reviews.