I think you're wrong on all but the last of those points - so at first Stalin had a pact with Hitler and it was the fact that USSR stayed out, that allowed the Nazis to sweep through Europe.
But then the big turning point of the mainland war, was when Hitler over-reached himself, took on the USSR at the height of the Russian Winter and lost huge numbers of troops - nothing to do with the US!
I'll give you Japan - but Europe was already decided before the US entered the war!
All that the US troops did was get to Berlin in time to divide up the spoils, start the Cold war and charge Britain huge amounts of money - which we only finished paying off, last year! So now at last, we owe you nothing!