Franklin cost the Western Confederate Armies what they could least afford to lose-LEADERSHIP...
The number of Command-level officers killed, Wounded and captured there made it nearly impossible for the South to put together much in the way of Unified and effective commands in the west, after that.
15 out of 28 Confederate Generals were casualties, and 65 field grade officers were lost.
It's as if the Confederate Army of the Tennessee had decided to kill itself by chopping off its own head.
Two weeks after Franklin the CAT effectively ceased to exist as a coherent command and two weeks after that Sherman was having Christmas dinner in Savannah.