A simple question: would you rather limit the carrying capacity for marines in trade of better gun stats or keep the current system where you can carry a boatload of shit but struggle at killing a drone?
By carrying capacity, I mean guns, ammo and all. A marine would only be able to carry one primary weapon and ammo would be limited mostly to belts; in compensation, damage, firerate and accuracy is increased for most guns and handguns get major buffs.
I personally believe the first option is the better way to balance marines. After all, the game is based on real life military, and as we all know, soldiers don't carry shotguns and rifles, nor can they fit extra ammo in their backpockets.
This would apply to other roles, such as specialists, engineers, medics, etcetera.