We sent the Soviets a lot, yes...but we were not what made the difference. All the Lend-Lease shipments did was to hasten the end of the war on the Eastern Front.
How do we know this? Because the first shipment of Lend-Lease aid arrived in Archangelsk on August 31, 1941, just before Operation Typhoon - Hitler's drive to Moscow - really kicked in. Thing is, Operation Dervish didn't carry nearly enough to make the difference in that battle. It carried wool, rubber, tin, and 24 fighters (with support personnel). Did that help? Surely. Did that make the difference? Not at all.
What did make the difference was the arrival of fresh winter-hardened troops from Siberia...and the Soviets' victory at the Battle of Moscow was the first real evidence that the Nazis were going to lose the war.
It wasn't our supplies that stopped the Nazis at Stalingrad or at Kursk, but leadership, courage, and a highly-effective intelligence network. Our supplies did help - no doubt of that - but what really saved the Soviets' logistics problem was when Stalin ordered *thousands* of factories to pack up and move to the Urals.
Lastly, whoever thought we could have beaten the Soviets if we'd attacked in 1945 was sadly mistaken - and it is an all too-common mistake among generals to underestimate the enemy. Unless we used atomic weapons (of which we only had a bare handful by the end of the year) we would have stood little chance of holding them in place, much less throwing them back out of Germany and Poland. This is all the more true since all their supplies were being brought in by rail, whereas we still had to bring in supplies by sea and air. What's more, the Soviet generals (and Zhukov in particular) had proven themselves to be excellent leaders - remember what they did against German armies led by Guderian and Mannstein.