I think this is the best angle of approach for this unit myself, and have no idea how the T-70 crew are reloading their 45mm gun* every 2s (down to 1.68s with vet...). The gun in real life had a rate of fire of 15rpm in the infantry version. The tank variant had a "semi-automatic" breech but I doubt highly this would be enough to double rate of fire for a weapon which still had to be loaded by hand and then also aimed and fired by the same crewman (2-man crew, no dedicated loader), who is also the tank commander...
*Wikipedia
Real life is not really applicable to a game like this. You can have a squads of soldier run up to eachother with SMGs and they will only start killing eachother slowly when they are within 10 feet of eachother. IS-2s IIRC only had a rate of fire of 1 round per minute because they had to load the shell in 2 pieces.
On Topic: One other solution I can think of would be to transfer some of the cost from Soviet T3 to Soviet T4. Then decreasing the cost and effectiveness of the T70 to be more like the Luchs. AA halftrack upgunning can be moved to T4 to ensure there is no opressive early mobile supression platform. This way Soviets get less shock value but earlier, and have access to the 7-man upgrade earlier to keep up with STG44/LMG42 upgrades. It might also create more of a window for the SU76, which is now always overlooked even for its intended role in keeping lights/mediums at bay, because currently the T70 already does that and T4 is just around the corner and it had better units anyway.