Why would you line up your own soldiers in front of your machinegun user, that makes zero sense.
While it is true that all of the other weapon types will have their own niche, buffing the lmg would leave it without any significant weaknesses while the others will have significant weaknesses (sniper rifles are tu expensive and doesn't beat out the other weapons at short range, shotguns are really poor at longer ranges, rifles are a jack of all trades but is beaten out by specialist weapons, etc) thus making the lmg the weapon of choice.