JFK is both underrated and overrated, IMO. He’s overrated because yes, he was handsome, charismatic, a good speaker and because his death impacted America’s largest generation in a huge way.
But I just got through reading a thorough account of his almost three years in office. He was a good President, probably in Bill Clinton’s class. He had an approval rating in the 60s and 70s, he was moderate on economics issues, liberal for his time on social issues, and a foreign policy hawk who nevertheless was cautious unless bold action was called for. He was not qualified for the Presidency when he first took office, which might have been why Kruschev tested him, but grew into the office pretty well. He probably got along with the Democratic majority better than any President in history, never needing to resort to the arm twisting and threats that LBJ did. That being said, he never tried to do anything as bold as LBJ. A lot more Clinton than LBJ or FDR, wanting incremental steps rather than big changes.
I think he’s also deified based on “what could have been”. JFK probably wouldn’t have achieved the domestic policy successes of the Johnson administration, but he also probably wouldn’t have had such an ill considered Vietnam policy. I think we still would have gotten more involved in Vietnam, but slow escalation wasn’t JFK’s style. It is more likely that we would have either had a more successful strategy or gotten out before tens of thousands of Americans had given their lives. But what Democrats really would miss is that JFK was persuasive and popular, which would have probably delayed the Democratic Party malaise of the 70s, which was caused in part by Vietnam but also by a government that had grown so fast that it wasn’t really doing anything well, and by political figures who simply were not very likeable. If we assume no assassinations, Camelot could have lasted until 1976, easy, with RFK succeeding JFK, and been as legendary as the FDR period.