Just out of interest, how easy were these tanks to produce? I'm just thinking along the line of thought the Allies may have accidentally done during WWII. My train of thought being, during WWII the Sherman was obviously no match for the Panzer tanks ect, there is even a famous quote by an American I think who said that Panzer (or Tiger) could knock a Sherman out with one shot from 2000 yards but a Sherman would struggle to that to the Panzer from 2 meters. The only reason why the Sherman came out trumps was that they very much out-produced the German's Panzers, for every Sherman taken out I think another 10 would come off the production line.
So this is what I'm thinking. The Communists obviously weren't stupid when it came to military technology, especially the Russians who had (arguably) the best tank technology during WWII. So they couldn't possibly produce an outright worst tank than the Western world, so maybe they went for the 'WWII' logic and created a rather good tank that could be easily produced in vast numbers quickly. Just a thought.