Except rifle grenade, who can deal pretty well with stationary m1919 squads. In fact, chosing this upgrade against ostheer it's not ...let's say... wise. It better works vs OKW.
If you stick to cover vs Ost it can be good. The low durability of Ostheer squads means that double M1919 in yellow or green cover knock Grenadiers down like bowling pins. Forcing them to use 30 muni, micro heavy attacks that you can dodge or mitigate with green cover is telling of just how much M1919s wreck.
I think mortars and mortar HT are the single best counter to double lmg Rifles though, so your right that going lmgs vs Ost is a very bad idea lol