McArthur was an old man when Korea was thrust upon him, the man was a general in ww1, (most decorated American officer in that war by the way)Truman administration screwed McAuthurs command in so many ways during that war that it bordered on treason. Just one example, all those Chinese troops that McAuthur had to fight were guarding against a possible invasion from Tiawan, until Truman order the 7th fleet to patrol the straight to make certain Tiawan did not invade. In other words Truman order American forces to guard the enemy flank! Freeing it forces to enter Korea, WHF!
Oh yeah....
I'm a BIG McArthur fan; warts and all - and he had many. For instance; he could be incredibly petty and usually quite pompous. While ruling Japan, he was derisively known as "The Viceroy" or "Emperor Douglas the First". (Probably by the same people that called him "Dugout Doug" during WWII.)
However, "military genius" is not vacuous hyperbole when applied to Douglas McArthur, and nothing revisionist historians can say will change that fact.