The thing about Napoleon and Caesar, neither of them won any truly stunning victories, the vast majority of their inflicted casualties were not in battle, but in their cavalry pursuing fleeing units and men being cut down during a route. Lee won actual battles, real fights, the majority of killing by Lee's men was done when the enemy had a real chance of winning, not mounted Germans or 10,000 Elite Cheval Cuirassiers or Lancers riding down fleeing conscripts or levied peasants. Cannae was also like this, a slaughter more than a real battle, but the slaughter was set up by a daring maneuver, which redeems the leader even if the overall killing is less impressive.