Gary,
I've come to believe that Albert Sidney Johnson was overrated. He was no doubt a tremendously impressive man in person -- witness the respect that Jefferson Davis and others held for him. But like everyone before the War, he had never really been tested. He handled Donelson poorly, and I was particularly stunned to learn that he had no idea that Nashville had been left undefended until he arrived there during his retreat from Bowling Green. His inexplicably excessive delegation to, and failure to supervise, Beauregard also contributed mightily to the confusion, delay and failure during the first day of Shiloh.
For these reasons, I wonder whether he would have had the courage to order a general withdrawal from the Shiloh battlefield after the first day.
One of the great ironies of the War is the fact that it showed that prior reputation meant nothing. The crucible of war exposed the shortcomings of highly-respected men such as Jefferson Davis and George McClellan; "losers" such as Ulysses Grant and William Sherman turned out to be the men who had what it took.
I don't mean to be too harsh on General Johnson. Virtually all generals, on both sides, appointed to major commands at the beginning of the War failed, probably because they had no opportunity to absorb the reality of how different the War was from their prior experiences. Second-generation leaders such as Grant and Sherman had the luxury of absorbing the scale of the war and learning from their experiences before they took command.