For the others, I disagree with some of your points and agree with others, but as far as I can see there is still a main difference in the sense that those others, for all their faults, are remembered for real and major achievements (which to be sure they may not deserve full credit for, but at least some), be it winning wars, obtaining the independence of their country, or putting an end to apartheid. I don't see anything that Kennedy could claim to have done that compares to such things.