JFK couldn't handle the replacement ambassador (Lodge) he spent specifically to overthrow Diem when said ambassador gave the go ahead and Diem wound up assassinated as part of the coup. Nor a 28 year old David Halberstam writing articles in the NYT about how American policy was failing without complaining to Arthur Sulzburger to try to get him fired. Actually, the press corp in general was his excuse for everything negative that happened, so they regularly black listed reporters, and the military was prone to "forgetting" them during trips in foreign countries. They also came down hard on figures who disagreed with policy on the record, Adlai Stevenson was banished from the White House or meeting JFK alone for this. (Not that in that case it probably wasn't a good idea since Stevenson was under the impression that the UN Ambassador was a constitutionally higher position than the President.)
JFK's objection to anything was that it'd get tied back to the administration because duh and used to harm him in his re-election campaign. It's why he refused air support for the Bay of Pigs even though it was the most essential component of the plan. It's why he backed publicly and then privately ordered nothing be done in Laos. It's why he refused to do anything about civil rights and even bitched to Wofford to get "them" to stop protesting so much. They bugged MLK not to blackmail him (though Hoover certainly did) but to find out his plans beforehand and try to block protests or get ahead of them in the press cycle.
JFK's foreign policy experience in comparison to LBJ was simply from being President at that point, he had accomplished almost nothing as a Senator or Congressman really. His brother did far more in less time (and Teddy did even more obviously) despite being hated by everyone. JFK's grand foreign policy achievement* was thinking of a quarantine instead of a blockade while trading already obsolete missiles out of Turkey.
LBJ committed to the consensus plan at the time (except for a few fringe members) that JFK was preferring to kick the can on as long as he could which was the fact that the South Vietnamese were failures and if the intent was to keep the regime propped up, it required American involvement beyond sending officers to lead South Vietnamese units that refused to fight. JFK had also stated the U.S. was not going to abandon an ally. LBJ also didn't give a shit that the U.S. would get blamed, especially after his 1964 landslide and then the Gulf of Tonkin Resolution. It still took him a whole another year to start bombing everything and dropping troops into Vietnam.
Before he was killed, JFK had agreed with military projections that a thousand U.S. "advisers" could come home at the end of 1963. Only half that number did, and 1,000 new ones were scheduled to be sent to replace them and fix the problems with the Strategic Hamlets which were working in the opinion of nobody except the White House, State and Defense Departments. (In fairness to State, and specifically Dean Rusk, JFK intended to be his own Secretary of State and Chief of Staff, so he constantly ignored any chain of command and regularly mused about eliminating the entire Department.)
Amusingly, JFK attacked Eisenhower and Nixon in the 1960 campaign for losing Cuba to the Communists, not ramping up assistance to allies like South Vietnam and Laos, the non-existent "missile gap" and so on. JFK's focus was on the Cold War and the Soviets. He considered The Guns of August, the most important book of all time (after The Bible anyway) and gave copies to everyone to read and digest as if it would provide valuable insight into the administrations foreign policy.
*Other than the Alliance for Progress, which LBJ immediately undermined because he thought the best person to handle it was a racist who hated Hispanics.
