The Army of Tennessee--not The Tennessee, that was a Yankee Army--never had the leadership it deserved.
I believe Sydney Johnson would have learned from his mistakes, but Bragg was bad news, Hood was worse, and J. Johnson was too cautious. And, IMHO, Beauregard would not have done much if he had stayed.
They, and the south, needed another Lee to command and and to get the other generals to work together.