Are you suggesting Truman was worse than FDR?
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.