“That said, most of the good senior officers at the beginning of the war were southerners.”
and most of those were made in the Mexican War, including Lee who was probably on the way out. He was just an aging Captain engineer building forts before the Mexican War. He had been passed over many times.
The only way to find the best leaders is to fire the bad ones and only stop when you get a good one. Beyond battle field success, mankind does not appear to have ever been able to devise a system that consistently produced master leadership.
Frankly, I think the real warriors get bored to tears during peace time and perform mediocre in what they consider to be unimportant tasks. They aren't necessarily winners in other fields or peace time drudgery, but when it comes to battle their eyes light up and they feel their calling. Certainly that's been my observation.