re: FDR was an awful president and MacArthur was an awful general.

Well, let's just go ahead and force ourselves into an extreme, shall we?

FDR was clearly seen as a great leader by contemporaneous Americans. That is something that should make one do a double take before declaring him "awful."
I'm not a fan, but I was born over 30 years after he died.
He was definitely an ideological Leftist, but thankfully the Supreme Court kept some of his worst policies in check. Huge government was really the result of World War II and the Cold War more than the Depression.
Social Security was a terrible idea and will have terrible long term consequences. HIs trust of Stalin was embarrassing, but at least he had Churchill to warn him and hold him back.
As Greatest gen and Boomers die off, his legacy will be seen as more of a mixed one as the longterm consequences of some of his legacy turn negative.

MacArthur is similar. His ego was unparalleled, even by Patton. He was a huge dickhead. Yet, his blowhard mentality worked in alot of situations. He was needed at the time and, at the end of the day, his leadership helped win the war. When it comes to Korea, he should have known his place. Andrew Jackson had the excuse of slow communications when he took the initiative to invade Florida, war on the Seminole in their own territory, and occupy Spanish Pensacola without executive permission to do so. Mac didnt have that excuse in crossing the 38th parallel. Even if Truman was skittish (arguable), you can't ignore a direct order from the President.