The Allies did not 'outplay' Nazi Germany. The Wehrmacht had very capable commanders that were in many ways more capable then some Allied commanders (when they weren't hamstrung by Hitler's unreasonable demands and intrusions).

The key to Allied victory was their industrial capacity, predominantly the industrial capacity of the United States. Even before Pearl Harbour, the United States was supplying Great Britain with weaponry and ammunition not to mention consumables such good which Britain needed if it was to continue resisting German aggression. Germany could not compete industrially with the Allies and while its industrial capacity grew during the war, it was never even close to matching the production numbers of the United States.

Germany also made a lot of errors when it came to the design of some their weapons. The Tiger Tank is a good example, often touted as one of the best tanks of the Second World War and superior to anything fielded by the Allies, the Tiger was an extremely expensive machine to produce, demanding large amounts of valuable production resources. It was also time consuming to maintain. The Allies on the other hand tended to field large numbers of weapons and vehicles that were relatively cheap to produce, easy to maintain while still maintaining a good level of operational ability. The Sherman Tank is a perfect example of this. While the Tiger was certainly a more heavily armed and armoured tank compared to the Sherman, the inability on Germany's part to produce enough Tigers to affect the course of the war made the far cheaper and easier to produce Sherman a better choice in terms of production.

When the Allies really began hitting Germany's industrial capacity by way of strategic bombing, German production fell, affecting their ability to supply their forces and in turn affecting Germany's ability to conduct the war.