How much differently would it have all played out if there hadn’t been a month delay to go stomp Yugoslavia and Greece for getting all uppity? The German army was about 60 miles from Moscow when winter set in and they didn’t even have winter gear.
The logistical contributions of the USA were also essential. Without them, the USSR could not have fought a war of maneuver.
USA donated items - 250,000 2.5 ton trucks - 12,000 jeeps - Thousands of C-47 cargo aircraft - Mobile short distance radio systems - The entire USSR battlefield telephone system.
Also, the USA and UK strategic bombing campaign froze 75% of German fighter aircraft in western Europe and 75% of anti-aircraft guns and 100,000 AA personnel. Germany could have placed an AA battery every 100 yards on the Eastern Front and increased their fighter and tank killer response by 4X times.