Let's begin with this question: what possible reason would the President have to allow WWII to go on an extra year or two???
1. There is no way to argue that one of these two possibilities is the truth:
a. either Franklin Roosevelt was entirely aligned with Stalin and the communist agenda...or
b. Joseph Stalin was brilliant and overwhelming in his manipulations of Roosevelt.
2. "But the USSR was our ally against Hitler! No. The USSR was not our ally. It was our secret master-manipulator. We were secretly master-manipulated, not into defeating the Nazis, who, but for the de facto Soviet occupation of Washington, I am now persuaded could have been eliminated in 1943, but rather into decimating,obliterating, Germany, Soviet Russia's natural barrier against expansion into its European empire. Japan, very much too, for that matter, in the East."
West, "American Betrayal," p.277
?
Your whole premise is based on the concept that we could have won the war without the USSR's help.
the reason why we insisted on the unconditional surrender of Germany was because after World War I, Hitler and others promoted the "Stabbed in the Back Myth" that Germany was winning the war, until Jewish politicians stabbed the Kaiser and the Army in the back.
We weren't going to give them that luxury.
Also, the reality is, most of the heavy lifting in WWII was done by the USSR in Europe. They engaged and pushed back 3/4 of the Axis forces fighting the war.
And it was the USSR's entry into the Pacific War that had more to do with Japan's Surrender than the Atom Bomb.
But we westerners like our myths about how we won the war.