Good reasoning, Gaveston. My guess is the biggest problem with the film of "South Pacific" is that Logan had done such a great job of fluid, almost cinematic staging of the piece on Broadway that he failed to adjust enough when directing for the camera. It's a very stagy film, although, to me anyway, the quality of the material does come through.
Andrew Samonsky replaced Matthew Morrison in the Lincoln Center revival, and I do not believe your problems are as much about him as you think. I loved Sher's direction, but his one misstep was to present Cable as a sort of ugly American. This was true of Morrison and it was true of Samonsky, and neither gentleman could make it work. Cable is callow but he is not callous. It was a more contemporary way of looking at American white men, but I don't think it was what Hammerstein or Michener ever intended and it did not serve the piece. Fortunately the quality of Cable's songs, particularly Carefully Taught, came through in both performances