“Arguably the best tank of WW-2 was the Russian T-34, which was diesel, heavier gunned, very fast and was the first to make use of sloped armor, which greatly improved protection.”
The Soviets didn’t seem to think so, because they used the Sherman tanks to equip their elite Guards Tank Divivions.
Only until such time as their productive capacity improved to the point where the T-34's became primary. I saw a number of T-34's at the Ukrainian War Memorial in Kiev. They are the roughest looking thing going because they had to be built fast with no "finish" on them.
When the Russians finally turned the tide against the Germans, the T-34 was their lead. That is the tank that won at Kursk.