Patrick Cleburne was arguably the best division commander of the Civil War. But for whatever reason (foreign birth? lack of West Point education? advocacy of enlisting slaves into the army?) he was never given command of a corps in the Army of Tennessee. He temporarily commanded an ad hoc corps at the Battle of Jonesboro and did not do particularly well, but it can be argued that the odd circumstances of that particular engagement were more to blame than Cleburne's leadership.
Suppose Cleburne had been given command of a corps of the AoT at some point in 1864. He might have succeeded to the command of Polk's corps after Polk was killed in June, Hood's corps after Hood took command of the army in July, or Hardee's corps after Hardee was reassigned in September.
How do we think he would have done? Would he have been as good a corps commander as he had been a division commander? Or would he have turned out more like A.P. Hill, having been promoted above his own level of competency?