Ding ding ding. We have a winner! If Shaq perfected the underhand free throw, he would be much tougher to guard. Fortunately, he's stubborn, and has a ego the size of Florida.
Hmmm...maybe you should look at what I quoted of your post. Plus, why would he bother to try it in private if his decision not to use the technique had nothing to do with its success rate? It's a moot point on your part.
Why? What Shaq said doesn't prove it would help him nor that he never practiced shooting them that way in private. In fact, Rick Barry said that he was told that one of Shaq's coaches did work with Shaq but that it didn't help, and, in typical Rick Barry fashion, he responded that it's because he had the wrong teacher. Maybe Shaq did try, like Wilt, and didn't think a point or two a game is worth the embarrassment, no one else in the NBA has ever since Barry retired either.
I don't think it would work. The ft line is simply too far away from the basket for the ball to get a nice bounce. The reason a layup works is that it is close to the basket. And the reason the bank shot works (i.e. Tim Duncan) is because of the angle of the shot.