The infantry is more abput humping 100 pound packs in 110 deg. heat than it is firing an M-16.
You sir are correct.
I used to tell my newbies that anyone can shoot a rifle or a machinegun, even drop a mortar. But can they hump that same M-2 or mortar, the ammo and the tripod or base up the 10 or 12 mile mountain trail at a quick march, use a pickax and e-tool to dig in a fortified position when the stop, and pull guard duty that night without falling asleep from exhaustion. All while humping their 60 lb turn out load, their body armor, water, beans and bullets. The average full ruck out was 120 lbs when I was in but we were mech infantry and had to carry more crap that most light units.
I had a Ranger come to my unit and complained that we carried more junk than anything he has ever seen. That was until we went to a gunnery exercise. After he saw a platoon sustain fire exercise he kept saying that he had never seen so much lead going down range at once.
Many newbies out of Infantry basic would struggle but make it past the fist day. And they had been training for 16 weeks. Some would even make it through day two and three of doing the exact same thing. Very rare was the soldier that can do that all week.
Few who have never done the work have even the slightest understanding of the whole body endurance and mental toughness that is required for the Infantry.