Regardless if Longstreet made the request Lee should not be sending his best corps commander that's just plain common sense , Lee was Davis adviser for nearly a year your telling me that Davis ignored Lee's advice not to send Longstreet? I find that far fetched imho.
From mid 1862 to mid 1863 Lee lost some 95k men according to Bonekemper and Gettysburg was just the icing on the cake , I have no doubt reading Longstreet's accounts he wanted to conduct a defensive war and grind the Union down bit by bit by having the Union throw themselves upon confederate fortifications or getting the Union to attack on ground favourable to AoNV.
Longstreet is not a machine he is a human being many of the high ranking officers who died over that year were his friends and unlike Lee who I find cold and detached I think Longstreet really cared for the troops under his command and realized the Confederacy was never going to win with Lee's reckless demeanour.
Maybe Longstreet hoped by going west he could ether replace Bragg or help Johnston into taking command of the AoT I know he had various plans that were thrown out by Davis who like Lee required more direct action even though the South did not have the resources to go on the offensive.
The cost of Chickamauga even with Longstreet's spirited punching attack was to great and only cost the South more heartache with the continuation of Bragg with Davis putting his personal friendship before his country.
BTW I really enjoy this thread I have learned a lot from yourself and others , I do read books but I have a very busy life so i do forget stuff you will have to forgive me for that.