Yeah and its mostly bullshit. I think part of why some of the northern generals appear worse is because many of them were ideologically against following up victories and capturing the confederate capital. MacClellan the first Commander of the Army of the Potomac was very against it and if I'm remembering correctly ran for election against Lincoln because of their disagreements over the war. But, there were also these supposedly "better" Southern generals who just charged soldiers into meetgrinders overcamd over for no reason, so it doesn't hold up anyway