Thomas was a very good good general, but it is generally agreed he often moved too slow.
Part of being methodical, I guess, but knowing when to throw the methodical part overboard and go for it is a big part of generalship.
And yeah, Thomas was rather methodical preferring solid low-casualty operations rather than battles of attrition. BTW, Sherman took his best troops, most of his artillery, and all his cavalry horses for the "March to the Sea."
Thomas reorganized and won the Battle of Nashville, a textbook victory, in his own sweet time, the most clear cut Federal victory of the war. Sour grapes for Grant and Sherman!