Strongly disagree. Truman faced the first instance of overt communist aggression in history as leader of a country that was tired of war and wanted no part of another one, as CIC of a drastically ill-prepared and diminished fighting force and as the first POTUS to have to wrestle the UN into action.
He met the aggressor head-on, checked his advances and pushed him back to square one. Any further action (cross the Yalu or drop the bomb) would have led to another World War with the US and UK (maybe) standing alone against China and the USSR.
It was Ike, not Truman who was POTUS in 1953 when the shooting stopped.
HST made his mistakes but his courage on Korea saved the world from global tragedy unpredictable only in its scope.
Truman does get credit for wading in .... but it's very much his fault that we did so at an immediate disadvantage.
I would say, too, that he badly misread the situation leading to the entry of China into the war. He had a lot of help there, of course, and it's probably the case that he could not have stopped the Chinese invasion. But we were not at all prepared for it -- in fact, Truman ignored a direct Chinese warning of intervention three months before they invaded.