The idea that Robert E. Lee was a military genius is the product of the same movement that seeks to paint the South as fighting the Civil War for reasons not pertaining to the enslavement of black people. He wasn't incompetent, he was solid (speaking in a vacuum), but even in the context of the Civil War, he wasn't head and shoulders above the field. George Thomas basically ended fighting in the entire Western Theater by his lonesome, leading to the entire Army of Tennessee being reduced to boots.