The Soviets defeated the Nazis with very substantial Western aid. The importance of the Western Allied contribution to the war was acknowledged in a negative way by Stalin, who spend three years hammering on about a Second Front. The Battle of Britain and the US and British Battle of the Atlantic not only absorbed a lot of Nazi energy and resources but also kept Britain as a forward post for the ultimate invasion of the continent. Meanwhile the British in North Africa performed a vital role in keeping Rommel's armies tied down and Mideast oil out of Nazis hands, while the American's tied up large numbers if Nazis in Italy. Nor can the importance of Normandy and the ultimate opening of the Second Friend be dismissed. The forces that fought the Battle of the Bulge were unavailable for stopping the Soviet advance from the East. The one Western contribution that seems to have played little or no role was strategic bombing. So if the Soviets won the war, they did not and could not have done it alone.
^^^^^^ CB: Agree with your last sentence and conclusion, but the Soviets did 90% of the damage. The US did the major damage to the Japanese.
The importance of talking about how much more the Soviets damaged the Nazis is to overcome the impression most Americans have that the US did most of it. The other important part is the 27 million dead Soviets. Americans have no way of understanding what the Soviets suffered. And the damage to the economy is not taken into account in assessing why the Soviet Union eventually ended. It wasn't because socialist organization of society is not viable ... as long as the socialist society is not bludgeoned with the biggest war in the history of humanity.