Nothing much would have changed had FDR been sterner with Stalin at Yalta. What leverage did FDR have? The Red Army of 1945 was massive, experienced, and well-led. Trying to dislodge them from Eastern Europe would have been difficult, and very bloody.
I suppose the western Allies would have won eventually due to their air power advantage. But no way would the American people have stood for it. “Your son survived fighting Nazi Germany. Now we are going to throw him into a meat grinder against a country that was our ally just yesterday.”
FDR also thought he needed Stalin’s help to finish the war with Japan. Stalin agreed to declare war on Japan 2 to 3 months after the war in Europe ended. He did keep that promise, declaring war on Japan exactly 3 months after Germany surrendered. But it turned out we didn’t need his help so much because of the atomic bomb, and that enabled Stalin to impose a communist regime in North Korea (as well as annexing a number of Japanese islands).
Eisenhower purposely held back "problem child" Patton who boasted he could be in Berlin in a few days. Not that impetuous Patton did not earn being disciplined, but it was Roosevelt whom Eisenhower answered to.