With regards to being head and shoulders above other bowlers, in my opinion he was. When one takes into account his dominance home and away and in all conditions, his stats (average, strike rate, wpm, 5 wicket hauls), contribution to team success, his aggression and tools he had at his disposal, no one can tick all the boxes he could.
McGrath, Steyn and Hadlee are the only ones who come close. Period.
McGrath didn't possess all the different tools that Malcolm had, let Steyn finish his career before we place him, but he is already in the discussion, but in a very strong team he just didn't put his team over the top like McGrath and Marshall did. Hadlee played in the same era and rightly or not was not seen as the best, being rated first being Lillee, then Marshall. His numbers, while also excellent, still is not quite as good as MM's. He was also similar to McGrath and not quite as versatile as Marshall.