When Barbarossa failed the war was lost by Germany. When Overlord succeeded the War was won (sort of) by the Western Allies.
Germany lost the war on the day they declared the war on the US in December 1941. Barbarossa and in fact the entire Eastern front qould be considered a rather bloody side show. It may seem counterintuitive, but Eastern Front was pretty irrelevant to the defeat of Nazi Germany.
There would have been no Eastern Front progress without the Western Front, but the Western Allies would be able to defieat Germany without Eastern Front. The reason is the quality disparity between German and Western Allies, particularly in the area of Artillery support and Air power.
Soviets had numbers, but they had very bad combined arms tactics which resulted in huge casualties. Any progrss on the eastern front only happened after July 1943 when the Allies landed in Italy. From that point Hitler lost real interest in the East and the best units were sent or held in the West. He was essentially refighting WW I when Germany lost in the West, but won in the East.