I think the part of the myth that needs to be busted is that hitting down on the top half will generate backspin. It won't. Maybe that came from golf where you're pinching the ball against the turf to generate backspin.
I don't dismiss the "hit the top half" instruction entirely, because it might work to help refocus the hitting spot for a kid who's popping up a lot. You don't want them to literally hit the top half, but you do want them to hit the ball higher relative to their pop-up swing.
I would echo this. Hitting the "top half" does not and will not create sufficient backspin to carry the ball. Just as hitting "under" the ball won't drive it to the outfield.
But, the brain stimuli of hitting the "top half" changes the hand path/bat path so that instead of hitting under the ball, the player can hit that sweet part of the ball that makes it go far. Over exaggeration helps players make the change.