That is vastly underestimating the Soviet role in the war. While L-L was a vital part of the Soviet war economy, especially when it came to supplying Moscow with resources to better funnel its remaining industry into armaments, the vast majority of the war effort was on the USSR's soldiers.
80% of all German troops post-1941 were focused on the Eastern Front, along with the majority of Axis forces except Italy. The Allies didn't want to open a new front on Normandy until they were sure the Soviets wouldn't get overwhelmed and get those Axis troops reassigned to the West.
And even with 80% of Axis troops in the East, it was not enough to break the Russians. Oh sure, the Soviets caught hell (27M casualties including 13-15M civilians), but they did it. They broke the freaking Wehrmacht. What the US "broke" in Africa and France were the bare remnants Hitler could afford to put there as a safeguard, and even that was a struggle.
Admittedly, a considerable chunk of US forces were in the Pacific, but that was mostly the Marines. The main focus was still on the European theater.
No, I'm weighting their effort accurately. Soldiers are meaningless without the food or weapons for them to fight. You are underestimating the role of the US in providing vital shipping, air support, naval forces, and yes even ground troops to the equation.
Something like 75% of the German army in 1941, less every year after that on average. As of 1943 75% of the Luftwaffe's fighters were on the Western Front, 40% of all the Luftwaffe had been killed off in Tunisia in 6 months, 80% of the German navy fought in the west throughout the period of the Eastern Front was going on, and even in 1941 of the total Wehrmacht less than half were in the East and that proportion dropped every year.
https://www.feldgrau.com/WW2-Germany-Statistics-and-Numbers
In Wehrmacht Service*, 1941: 8,154,000+
*Includes
Wehrmachgefolge - those considered armed forces auxiliaries and in the direct employement, assistance or aid of the Wehrmacht, but not considered part of the
Heer,
Luftwaffe,
Kriegsmarine or
Waffen-SS. Inlcudes those from groups such as the RAD, NSKK, OT, etc.
https://en.wikipedia.org/wiki/Operation_Barbarossa
That's for all Axis powers that participated in Barbarossa in June 1941, not just the Germans, who made up somewhere around 3.1 million men. Out of 8.1 million men in military service in 1941.
Of course you're leaving out the role of the UK in this, as they had inflicted over 2000 aircraft losses in 1940-41 just over Britain not counting what they did in France, the Mediterranean, or the Balkans. That also leaves out the role of the British in blockading Europe and effectively leaving it in famine as of 1940, while also shipping L-L to the USSR in 1941 before the US.
Then there is the role of the USAAF and RAF:
https://en.wikipedia.org/wiki/Defence_of_the_Reich#Defeat_(1945)
Don't forget the impact of bombing of industry, cities, and oil, not to mention transport, which ultimately collapsed the German economy.
Meanwhile on the Eastern Front:
http://chris-intel-corner.blogspot.com/2012/04/eastern-front-aircraft-strength-and.html
The USAAF alone destroyed 300% more Luftwaffe aircraft than the Soviets; with the historical exchange rates, if the Luftwaffe had been more present in the East Soviet losses would have been much worse from 1943 on. Since Soviet Deep Battle doctrine depended on air superiority if the Luftwaffe is present in the East in strength even with LL the Soviets aren't going to be pulling off their deep advances.
https://media.defense.gov/2017/Mar/...LD_BROWER_CANBY_AIRPOWER_MANEUVER_WARFARE.PDF
35. An interesting statistic is that 11 percent of German counterattacks were in the battle for the first position, 58 percent for the second, and 30 percent for the third position. Thus, about 89 percent of the counterattacks had to be repelled beyond the limits of the first position, that is, where the enemy reserves were not dependably neutralized by fire during the period of artillery preparation.
To evade the superior German fighters, minimize aircraft losses, and enable downed pilots to be rescued, the Red Air Force generally limited its attacks to within 10 kilometers of friendly lines,42 a method that had the further advantage of helping draw the enemy into antiaircraft fire traps. To the extent that 90 percent of Soviet aircraft downed during this period (the summer and autumn of 1941) were lost over Soviet territory, these tactics worked. 43 On the other hand, most German combat losses were caused by ground air defense.
42. Ten kilometers is not restrictive when considering the fact that the Russians were mostly concerned about protecting their own troops from the Luftwaffe and from the very beginning focused their ground attack upon the thrusting German tank pincers (often ignoring marching infantry). Ten kilometers could thus be from the deep flank as well as the front.