The USA provided Russia with 100% of its 2.5 ton trucks, 100% of its jeeps, 100% of its cargo aircraft, 100% of its battle field telephone and radio communication system, and huge supplies of diesel and aircraft fuel.
In addition, the USA and English air forces maintained relentless pressure on occupied France, on occupied Italy, and on the German homeland.
The Germans had 15,000 anti-aircraft guns and 100,000 AA troops in western Europe.
The Germans also had 250,000 front line and reserve troops stationed in France and Italy, defending against an Allied land invasion.
If the Germans had enjoyed the luxury of a neutral USA and a pacified France and Italy, they would have destroyed the Russian army and air force, and occupied Russia from St. Petersburg to Moscow, and all of Ukraine.
Still, I believe that the Russians would still have won in the end.
You cannot control a land mass as large as Russia. That’s why the Mongols never tried to rule Russia directly-they regularly exacted tributes, but otherwise left the Russian principalities alone (Russia was not yet united as a polity then).
The numbers for vehicles is staggering. 750,000 trucks. Most made by Studebaker. The Russians actually built a monument to Sgudrbaker. 7,000 P39 and P63 Bell fighters. 3,000 A 20 bombers. 100 Octane aviation gas. And the list g goes.
Still it must be mentioned that for every German soldier in France and the Low Countries on June 6 1944 there were three on the Eastern Front. Without Russia the Allies never even get off the beach.