Which is perfectly safe to stand under because its terrible rate of fire LOL. You dont play 1v1. Team games all kinds of rules apply. In team games individual performance isnt as important.
Grens and Cons are the basic infantry. They are the counter to support teams. If Grens can kill 6 models JUST AS FAST as Cons can kill 4 the only thing left that applies in terms of surviability is HE. If there is a tank in your face or a mortar barraging your mortar and you havent moved it...its L2P. So the benefit of having 6 men vs the benefit of having over 300% better ROF are not equal.
If we are talking about kill power the Soviet mortar is more likely to kill more squads because it's shooting at 4 men squads more accurately so it doesn't need to fire as fast. Wether I play 1's or not it's relevant to the discussion at all.