1. Maybe. In order to buy this, you have to interpret every contingency in JFK's favor, regardless of plausibility:
Examples:
-Diem's host/sponsor in the late 1950s (JFK) suddenly became willing to change his own lons-standing Vietnam policy, the "failure" of which would have his hand-prints all over it. -The man who refused to withdraw in 1961, when there were US 1,500 troops in VN and Ike could be blamed, suddenly became willing to withdraw all 17,000. -That the "phased withdrawal" scheme would have been unaffected when it became obvious that RVN troops could not do what US troops were doing.
2. Fact: It didn't happen. What was semi-ordered was a sneaky semi-withdrawal of 1/17 of US troops.
3. Who cares? Kennedy sponsored the beginning of the war in the 1950s, when he was a war-mongering Senator. As President, he escalated the war by a factor of more than ten, both in terms of troop levels and rules of engagement. He never clearly and decisively ordered a single troop to withdraw, and he never had the spine to say anything decent in public. His overall Vietnam record is of huge war crimes. Maybe it would have worked out slightly better than Johnson's or Nixon's, but they all belonged in a deep, dark jail cell for their actions. Galbraith is fine, and his dad's awesome, but why waste time trying to rehabilitate scumbags who did such unconscionable things?