Eisenhower was in charge of D-Day, arguably one of the most complex human endeavors. He made the majority of the decisions surrounding it, of course influenced by outside factors (De Gaulle, Churchill). He chose Normandy, he decided which units would go where, who would lead the campaign on the ground. Incredibly important decisions, yet he left the tactical decisions to those on the ground. Delegating broadly, as a good commander should.

General Marshall, Eisenhower's superior also delegated broadly, while making key decisions as to the timing of the invasion, which units would be involved, and making sure all the disparate organizations involved were used to the best effect. Again, delegating broadly, as a good commander should.

This goes on and on up to Roosevelt himself, the Commander in Chief at the time. Does he know jack about the tide tables on Omaha beach? The range of a German 105mm howitzer? Of course not. Yet he clearly mandated the important decisions.

All three of these leaders were clearly EXTREMELY competent.