I think that historically the USSR had many more light tanks than they needed. That's why they converted them into SU-76's, of which they had enormous numbers and used them throughout the war.
So maybe the better solution would be to increase the USSR light tank production, maybe decreasing the medium tank production a bit until 1942, when it needs to really take off. Looks like they were doing about 100 T-60's a month historically in 1940/41 ramping up to 400 by the beginning of 1942. T-70 production was like 400 a month in 1942, down to 300 in 1943. In 1944, SU-76 production took off at about 600 a month. So right now, looking at production in the game in July 1941, there are about 200 T-60's being produced a month. T-70 factories are going to add about 250 starting in the winter of 1941/42, which seems low.
I'm also seeing there's a T-50 factory still in production, and from what I've seen, historically T-50 production stopped before the war broke out and only amounted to about 60-100 total anyway. So maybe convert that Moscow T-50 factory to T-60 and increase it to 30 a week starting in August? That would bring production to 400 a month by January 1942 assuming that something has to be evacuated. Then more or less double the productivity of the additional T-70 factories and it should be about right.
On medium tanks, the game has about 400 T-34's coming out a month. That is a little higher than the historical 1941 average, which is about 250 a month, but taking into account evacuations, that's about right. The Kharkov factory is most likely going to have to move and be out of business for several months. So getting to the historical 3000 produced for the year the game production level is probably about right. 1942 T-34 production was almost 13,000, and 1943 is almost 17,000. So those factories need to get much more productive later or maybe new factories come into being. I've never played that late in the game so I don't know how things work them.