Johnson was an infinitely greater, albeit deeply flawed, president. Vietnam destroyed his presidency and it would have done the same to Kennedy's, had he lived.
Inclined to agree, though many historians doubt Kennedy would've gotten us into the level of involvement in Vietnam that Johnson did; Kennedy recognized how unpopular our presence was in the region and had no hope that would change, while Johnson regarded Kennedy's trepidation as weakness (despite agreeing, at the time, that this was primarily 'Asia's war to fight'), and the two men often clashed over it.
I think it's difficult to fairly evaluate Kennedy's record on civil rights, which tends to be the main prism I see him through, from the vantage point of today. He was certainly stronger on civil rights than his opponent, Nixon (his intervention to get MLK out of jail in Atlanta, 1960, endeared him to many African-Americans), and it was Kennedy who in June 1963 got Congress to begin deliberations on the legislation that would become the 1964 Civil Rights Act (hence Johnson's charge to Congress five months later: "No memorial oration or eulogy could more eloquently honor President Kennedy's memory than the earliest possible passage of the civil rights bill for which he fought so long"). But it's also true that behind the scenes Kennedy often dragged his feet for fear of splitting his party, and over time alienated many civil rights leaders by repeatedly lecturing them in private meetings to be patient, don't make all this trouble with marches and sit-ins, can't you see my hands are tied here, etc. etc. There's a reasonable case to be made that without Johnson's far more forceful style and Texas grit driving it, that legislation might never have passed at all, or become pitifully watered down. ("Now John...you've got to go back and get those boys by the
balls. Just like a bull gets on top of a cow...and you've got to
squeeze, squeeze 'em till they hurt," Johnson told a startled John Lewis, then SNCC chairman, at their first meeting in 1965, urging Lewis to immediately put the newly passed Voting Rights Act to the test through renewed voter registration drives in the Deep South.) But Johnson himself repeatedly dragged his feet behind the scenes too, had personally obstructed civil rights legislation as Senate majority leader in the past, and alienated civil rights leaders more than Kennedy had by cold-shouldering the MFDP delegates at the 1964 Democratic Convention. Even so, like Kennedy, he was unquestionably stronger on civil rights than his opponent, Barry Goldwater.
Mostly, I see Kennedy's iconic status as less a comment on him than on our nostalgia for Americans' outlook on themselves and the world at that point in history. Ot at least, how we imagine that outlook to have been. I remember that my parents considered his death a great tragedy for the country and an ominous foreshadowing of what was to come (MLK, RFK, Vietnam), though they never idolized or venerated him the way some of their friends seemed to.