I guess there is some historical accuracy to hip fire MGs but aimed shoulder fire, come on!
It isn't impossible but imo that is not the point. The question is: How do you set apart MGs gameplaywise, especially compared to smgs?
One rule of FH2 weapon coding is that damage depends on the round fired, so lmgs do the same damage as rifles. So they need a drawback compared to pistol ammo automatics. For lmgs like the Bren that means: Higher spread when hipfiring and moving, slower ironsights. The weapons are supposed to feel more unwieldy, less "run and gun".
For the gpmgs this was made even more extreme since the fast rof and large mags make these countermeasures ineffective. I mean even know you can dolphin dive with them at close range despite the huge deviation penalty after proning.