MacArthur’s command was vast, and he fought the Japanese whose tactics were often futilely suicidal. The Kamikaze planes were an effective, and frightening, tactic. Banzi charges simply spilled blood. In Guadalcanal, Japanese tactics could have hardly have been better chosen to insure the maximum number of Japanese causalities. Still some of the elements of his command must have suffered a better ratio of friendly to unfriendly casualities than others, so at least some of his subordinates would have had to have outshone him in that statistic.
Patton did manage to create or exploit dynamic situations, were the enemy was in retreat, which is the best time to inflict high casualty ratios. He is is probably also credited with casualties caused by Air Force units, attacking German units he faced. When the Germans tried to run on the road in daylight they were sitting ducks.
What you said was equally true of the other American field generals in Europe. Patton wasn’t fighting a retreating army in North Africa where is changed the whole dynamics of the American invasion of Casablanca. He did a number on attaching (not retreating) German armor at the Battle of El Guettar in Tunisia. I won’t go into Sicily where he outran Montgomery, or his roll in halting the Germans in the Battle of the Bulge. Using the tools available and creating or exploiting dynamic situations is what make a great general and saves troops.
MacArthur’s strategy of bypassing Japanese held islands, cutting off their supply, then going back and mopping them up was responsible for his success.
Some of his own casualties were also caused by Air Force units.