In the trenches of France, it was an unshootable POS and the Canadians swapped them for Lee-Enfields just as fast as they could. Point being that conditions of use matter more than anything else.
I own a few AR-15s, but the things I don't like about them are functions of the basic design:
-I find the charging mechanism to be a pain in the ass, as it requires dismounting the weapon to use.
-I don't like the enclosed receiver that makes dealing with a jam tough (and any weapon will jam when debris gets in it).
-The direct impingement gas system increases the amount of troubles you are going to have to deal with, because it brings everything right back into the receiver and mag.
-The 5.56 is inadequate for shooting through things, which provides a lot more usable cover to the enemy.
Per the tests you referenced, firearms that are shot continually (staying hot) will put through a lot of rounds without issue. While that same gun will jam on a fraction of that many round if allowed to cool off without cleaning in between. Similar to light bulbs and car engines, its the starting and stopping that induces problems.
Is the AR a POS? Well, I wouldn't own several if I thought it was a POS, the recoil is non-existant and volume of fire is high, but its certainly not my all around favorite.
These weapons did not cool off in the firefight referenced. It was sustained fire that was blamed for the jams. The AR platform is not perfect. I own several myself along with other weapons but Stoner did not design or build a pos. I will take an M4 over an AK any day of the week. I can strip it, clean it and repair it blindfolded and I can keep it clean enough to function in a firefight. I can shoot the eye out of a gnats head with it. My favorite is a 7.62 in the AR platform... scratch that... My Serbu .50BMG is my favorite.
LLS