Your suggestion makes sense on why someone might want FDR around longer. I can’t imagine holding that position, but there are many things I can’t imagine that other people think are true.
If one were limited to choosing American politicians that one wished had died sooner, I think he would be making a lot of lists (FDR, not Truman).
I kind of wish that Jefferson had died just before the Louisiana purchase—while it was a great deal in many ways, it kind of undermined the strict constructionist position. I have a huge admiration for Jefferson, but view the act as something of the equivalent of the original sin against the Constitution. Being patient and finding a way to do things correctly, I believe, might have made a huge difference.
The British would have grabbed it all & with their fleet enforced it!
An Indian Confederation counterweight could have been formed with British help - think Tecumseh and his efforts.
Western expansion would have been harder, bloodier & and an international issue since the British were involved.
I have mixed feelings on FDR, I think he was a good wartime President, but he did have some bad actors in his Administration, I don’t know who could have done a better job during the War, amongst his contemporaries, it wasn’t as if the Republicans of that time were much better, Wilkie was a joke.