The questionnaire on weapons was to find out opinions of issued gear. The M9 was panned, not so much due to caliber, but to magazine failures, and worn-out guns. You can only rebuild an aluminum framed gun so many times before the wear on the frame begins to interfere. Ask Vickers. Those soldiers who used a .45 ACP in issue weapons felt it superior to the 9x19.
The M16 was actually liked better as far as ammunition performance than the M4. The M4 scored higher in CQB, due to the ease of movement.
Those issued the M14, after receiving enough magazines and support gear, found it to be an improvement over the M16 in the DMR role. How much of that was subjective, and based on presumption is anyone's guess.
The M249 was a mixed bag, usually due to the age and wear on the issued weapon.
The M240 was considered too heavy for dis-mount use. The Product Improved M60, while in small supply, was liked over the M240 by SF forces.
I'm too old for formal combat today, and won't be visiting overseas any more on Uncle's dime. I'm not constrained by Hague or Geneva, or the UN, so I really have no dog in this fight. I will say that it seems that any adverse comment about the M16/M4 family is met with more opinion than fact today.
Face it, the veterans of past wars in which the United States was involved has less support, and many had more contact time than today. Their weapons were in more use, and the cleaning regimen was less intensive than today's. That says something about the current issue weapon. Even in WWII, in the desert, the M1 Garand, the M1 Thompson, and the M1 Carbine required less maintenance to function than the current rifle. Yes, there were failures, and they were noted and acted upon, not excused as the fault of the troops.
The British Sten, and Bren guns were also no strangers to the sand, and they required less maintenance to function. The FAL has it's bolt slotted to allow it to operate in such conditions. Yet, after 40+ years, our issue rifles are still less considerate of cleanliness. With our increasing use of Reserve and National Guard troops, the idea that maintenance is a personal, and leadership, failure is a poor one. It's an after the fact conclusion that does nothing to save lives or material. There has to be a better way, and a better design.