I think the difference in philosophy between players who are motivated by individual accomplishment and those who are motivated by team success is critical. Any game must choose one or the other, and balance on that basis. KCIV tells us that six magazines give him too much latitude to camp a FOB and rack up kills. As an automatic rifleman, I expend six belts of ammunition routinely in an engagement. Does that mean I'm getting too many kills, and need to have my ammo capacity nerfed to bring the game into balance? No. It means I'm suppressing the enemy so my squadmates can move. Putting rounds into an empty window doesn't get me a kill, but it keeps the window empty. I can't do that with thirty rounds. Neither could riflemen whose ammo capacity was limited by the weight of 7.62x51, hence 5.56x45. A squad succeeds through maneuver. An individual succeeds through other means.
The question is simply this: what kind of game does Squad want to be?