Ive been wondering this too. But then i starting thinking about the other protagonists of the older FE games. Like Marth, Ike, Sigurd, Elwood. Were tactical geniuses like Robin? Or were they in the same boat as Corrin?
But if you ask me, Corrin is just the guy who has the final say. Since the very start, hes always getting help forming stategies with the other members. Gunter, Leo, Subaki (i would guess) come to mind. They do have a lil something called a war council that anyone can join in.