Johnston hated Davis and the feeling was mutual. That put a crimp in any command he held.
Johnston was an excellent general at staying in the fight, but somehow his brilliant maneuvers always wound up with him retreating. Admittedly with minimal losses and his army intact to fight another day. But always retreating will eventually lose you the war.
It is likely the Peninsula Campaign of 1862 might have had a quite different result had Johnston remained in command and not been replaced by the infinitely more aggressive Lee.
OTOH, Hood showed what could happen when Johnston was replaced by a more aggressive but less effective leader. But then it's difficult to see how the Atlanta campaign would have ended any differently had Johnston remained in command. Just would have taken longer.
I've been thinking recently about how differently either Antietam or Gettysburg would have turned out had Grant, Sherman or Thomas been in command of the Army of the Potomac. Lee was lucky in his opponents.