I love Monday morning quarterback what-if threads.
You cannot examine any historical event, or the leaders during that time period, in isolation. WW2 is arguably the greatest failure of diplomacy in modern history. Reparations against Germany after WW1 and European imperialism in the far East are what set the conditions for the rise of Nazi Germany and Imperial Japan.
Similarly, the failure of the Allies to open a western front while the Soviets absorbed the brunt of Nazi aggression is partially to blame for Stalin's increased paranoia towards and animosity against the West, which set the conditions for the Cold War beyond the ideological conflict between communism and democracy. Arguably, Stalin was a greater tyrant then Hitler, yet he was our ally against a common enemy, and proved to be an even greater threat in the long term.
There is no question that WW2 was a just war...does FDR deserve all the credit? Hard to say. Would things have been different in the European theater without the likes of Eisenhower, Bradley and Patton providing visionary military leadership...or MacArthur in the Pacific? Similarly, we have Hitler to thanks for over extending his military and setting the conditions that ultimately enabled an Allied victory. Would we have broken the fighting spirit of the Japanese without the atomic bomb? Again, hard to say.
Let's look at Islamic fundamentalism now, again something that didnt emerge in isolation of other events. The fall of the Ottoman Turkish Empire, and the arbitrary carving up of the Middle East by Europe, is what set the social conditions that entrenched Islamic fundamentalism throughout the region. Cold War politics only further heightened Islamic distrust of the West, which gradually shifted to hatred over decades of failed foreign policy engagements.
Taking all of these things into consideration, Bush failed to react to the world around him, and has perhaps made things worse. Would things be different if FDR, Reagan, Bush I or Clinton were in office...or Al Gore for that matter...again, hard to say?
Would Afghanistan would be different if Patton was on the ground there...or what if Eisenhower was in charge of the Iraq mission?
We can play out such scenarios all day...but they typically don't make for very compelling discussions as there is no factual basis to them, ultimately limiting the debate to partisan jabbing.