In an environment involving nonstupid players, not having your grenadiers move is a trivial excercise. Additionally, range is everything in this game and soviets always have to close in, so it's very easy to predict where is moving when towards what.
If they won't move they will get punished by mortar or by thrown molotov. I've never said to try to throw one with a squad that is under LMG fire.
Hell even Maxim on max range will neglet LMG dps rendering it useless. There are so many options the devil is in the details as always. Play smart, think, set traps, use your units effectively and try not to waste them.
I agree Cons are medicore late game, but there are so many AI options for Soviets late game that LMG becomes irrelevant.