Longstreet should have been put in charge of the Army of Tennessee. He couldn’t have held Atlanta, either, but he was brilliant on the defensive and might have held it at least until the November elections. Absent the fall of Atlanta, Lincoln might not have won. Lincoln himself, that summer, was convinced he would lose. Atlanta changed everything for him.
IMHO no one could have saved the south much less Atlanta. The south did not have the combat power to succeed. Especially in the west. To think otherwise is a romantic delusion. As a southerner I once suffered from the delusion but not any more.