Professional card players do not handle cards like either laymen or magicians. Real hand mucking is designed to emulate the actions of professional card players, and does not look "natural" in the way magicians think of the term.
Good hand mucks (and those of Giorgio and Forte certainly fit that definition) are invisible and take place so rapidly and efficiently that it seems impossible anything could have conceivably happened.
But there's a tremendous difference when a magician does a hand muck as opposed to a professional card player. If a pro card player moved as slowly as a magician in switching cards, it would attract attention because the handling would be unnatural in that milieu.
Gene Maze did beautiful hand mucking, but it was for magical purposes and wouldn't pass muster in a game because he didn't handle cards like a pro card player.