If I could stay off topic for a brief while.....
I don't think it fair to compare the Sherman and T-34, at least in terms of anything other than them both being mass produced, and therefore "cheap". The T-34 was a far better tank than the Sherman. When the Germans first encountered the T-34/76 in 1941 it came as a shock. With its sloped armour and 76mm gun, compared to German tanks with vertical armour and 50mm guns, it outclassed everything the Germans had. It was the encounter with the T-34 that led the Germans to develop the Panther and Tiger in the first place.
By the time that Shermans reached European shores, the T-34 had moved onto the T-34/85, which had a 85mm gun that was certainly capable of taking out Panthers.
So, in June 1944 the Allies had poorly armoured and armed Shermans, while the Russians had better armoured and armed T-34/85s.
The Allies relied on Tank destroyers, and in the Brits case Shermans armed with a 17pdr gun, "Fireflies" to take out German tanks.
As for the Russians effectively winning the second world war, they pretty much did. The much vaunted "North African" campaign never involved more than a handful of German Divisions. As for the invasion of Europe, I read somewhere once that at least 5 times as many German divisions were destroyed on the Eastern front compared to in the West. This link shows where the bulk of the German forces were deployed.
Number of German divisions by front in World War II
I should point out that:
I'm not Russian
I'm not trying to bash the Americans (or indeed the Brits).
I'm not trying to denigrate the contribution made to the war effort by Americans, Brits, French, Poles, etc, etc...
I'm just trying to stick to the facts, which are that the Russians broke the back of the German armies - a fact that is rarely acknowledged in the West