Calling Kennedy our greatest president is a bit of a stretch.
Visionary? Yes.
He did win a showdown with the Russians on the Cuban missile crisis.
Now, on to the bad. While troops were going to Vietnam during Eisenhower's presidency, Kennedy truly set the tone for the Vietnam war. The difference was he didn't live long enough to have his reputation completely demolished by it. He cheated on his wife in office. He was a drug addict. History has just been very kind to the man, but if he were president today, he'd be torn apart by a much different media. Remember, electronic media was brand new then, and there was still a lot more censorship in the news, and newsmakers cared about the reputations of our politicians, unlike today.
A list of great presidents of the 20th century to me would include both Roosevelts and Reagan. Say what you will about Reagan, but his final standoff with the communist block brought the eventual downfall of Russian domination in eastern Europe. To me, that's a larger accomplishment than a 3 day standoff with Kruschev.
Still, your post makes some very valid points about the current state of affairs, and I can appreciate your perspective as an outsider looking in.