I still think the best decision would be to throw out the idea of choosing one tier or the other.
Swap the T34 with the SU-76 (maybe increase its penetration?) and then make the T3 building cheaper/T4 more expensive.
Soviets would then have a mid game opportunity to push the Germans off the map with light vehicles or play it safe and go straight for the "heavier" vehicles (none of which are still as good as the German equivalents).