StGs are way too strong for all of five volks and splitting the squad up is extremely inelegant. The currently proposed method makes the upgrade either a no-brainer or a waste of munis, instead of a solid strategic choice. It's just not conducive to balance.
We've had LMG42s on Grens for ages, and LMG34s on Obers a bit less than that, I'm not seeing the issue with adding more no-brainer upgrades. If we actually got rid of some, sure, awesome! But we certainly haven't been.