Ever ran with a machine gun?

The fact the women seem to have done as well as men wrt hit probability using the M4 but not the heavier weapons, really point to physical limitations and not lack of skills.

The casualty evacuation issue is also a major issue, men can carry both sexes, women will have trouble with many men, and will be completely unable to move the bigger men...

From personal experience in target sports, strength and fitness plays a surprisingly big part in weapons use. Being able to handle a weapon with the least of effort while maintaining a low heart rate makes aiming a lot easier.