Red storm on the reich KU History book says:
70% percent of all combat deaths on the Eastern Front
80% of material loss on Eastern Front
75% of civilian deaths on Eastern Front
If it werent for 10 years of Japanese atrocities in China, the above numbers would be nearer to 90%. WWII could have actually been called the Great Russian and German War had the US not been involved.
And Stain is much to be blamed for that for ruthlessly executing generals etc. and not being prepared for war with Germany, and then blaming his leaders for losses.
Brute Force by John Ellis is a good book about the war detailing the impact of Russian front and overall allied production.
The US provided the Russians with transport vehicles but their tanks were primarily Russian.