Target-wise the closer to the Bull's eye you get the better you are. How do you measure assault weapon skill? By the numbers of kills/sec?

The skill of any weapon is judged by how close you can get to the target.

From what I've read ... the military went with the M16, because the lighter rounds allowed the soldiers to carry more ammunition.
The goal of full-auto weapons is not so much to kill the enemy, as to suppress them.
In other words, send so many bullets towards them to force them to keep their heads down ... until your "designated shooter" can get close enough to kill them.

The whole theory only makes sense if every army uses the same thinking.
It doesn't work against a military where every soldier is trained as a marksman.