I think most of that was joking.
When we carried our dismounted loads, they came in drums, (or for us and our cobbled together dismount 240, boxes).
The problem wasn't so much the weight but the form factor and the environment we were operating in. The bulk factor made moving through urban environments quickly a problem, in ways it wasn't during training in other environments, as it fucking caught on everything, and buildings and brick don't give like small branches, it made getting into some really good firing positions cumbersome and 'slow', when every second mattered. We had to pick between a tradeoff of ammo accessibility or fire position accessibility. I think this might be why they chose to break up the load in magazines instead of drums.
Although thinking back on my comment on the rounds I expended in my engagements, that wasn't a very applicable example, as I was just one machine gun, out of 3 machine guns on the tank, out of 4 tanks in the platoon, 2 of which per tank were stabilized firing systems with ridiculous accuracy (I had a hobby of drawing faces to check how tight my zeroing adjustments were). We collectively expended metric fucktons of ammo a dismounted squad couldn't hope to match.
