I just think that Soviets should be more flexible in dealing with a variety of things Germans can throw out. Having specialized tiers is fine as long as Soviets can jump from one to another without suffering huge setbacks.
Just a random idea, what about having an option to convert your T3 to T4 and vice versa for some fuel and MP cost say 1/3rd of the building cost and say this can only be done once per game.
Or reduce T3 or T4 cost by say 40-50% if T3 or T4 already built? This gives soviets less flexibilty but doesn't doom them if they need to adapt later in the game.
Cant see this happening though tbh.