If your understanding is that the chief of staff of the United States Army was responsible for the decisions made by US naval commanders in the Pacific in 1941 or the Atlantic in 1942, you may need to read more...
Beyond that, MacArthur was the commanding general of the military advisory group that "organized" (to use the term loosely) the PCA in 1935-41; he was theater commander for USAFFE in 1941-42; and he was SCAP in the Far East in 1950-51. His failures to match strategies to resources in all three posts are a matter of historical record.
One can pretend otherwise, but the historical reality is undeniable.
In his favor, Mac was a capable combat commander at the brigade/divisional level in WW I, and a relatively capable Army CoS in peacetime in the 1930s. He was fair as wartime theater commander in SWPA in 1942-44, and good as the peacetime occupation commander in Japan in 1945-50.
In comparison to his US flag/general officer peers engaging in coalition warfare at "relatively" the same theater-level of responsibility and complexity in WW II, (Hart, Nimitz, Eisenhower, maybe Ghormley and Halsey in the SWP) the only one he really outshines is Ghormley, and that's faint praise.
In terms of a wartime SCAP in the Far East, Ridgway was heads and shoulders better than MacArthur.