The US provided a tremendous amount of food to the Russians. Who had just burned half their country, and a lot of their farmland to starve the invading Germans. 4.2 million tons of food is ALOT.

The US provided 2/3 of the trucks used by the Soviets ( 409k), which allowed the Soviets needed to move men and supplied quickly, which was huge in their quick counterattacks.

The US also provided an incredible amount of Oil and Steel that the Russians needed for their supply lines. The US produced the majority of the trains, and rail used to move supplies to the front. Logistics would have been an absolute nightmare with out functioning railroads, and trucks to move supplies. The Russians had limited Steel and Oil.

The US sent huge amounts of aluminum, copper, steel to the Russians. More than half of the metal the Russians used for Production came from the US. So even though Russia produced most of their own planes/tanks they did it with American raw materials. Russian production of plane/tanks would have been less than half of what they were without all the Metal sent from the US.

Yes, Obviously the 2 front war was huge, and I agree the Germans made some significant errors, but Lend Lease was not a minor factor. It transformed the Russians ability to move men, equipment, and supplies quickly. It also allowed their domestic production to focus more on tanks/planes because they didn't have to build hundreds of thousands of trucks, trains, rails, food, clothing etc.