Kutuzov is an old general brought out of retirement to be the commander in chief during Napoleon's invasion, and he does a pretty bang-up job with it.
While Tolstoy brought Napoleon down a notch in this novel, with Kutuzov we see that the bringing-a-mythological-man-down-to-earth thing can actually work both ways. Tolstoy turns the historical Kutuzov into a wise old soul who can commune in some mystical way with the general day-to-day feel of the army and guide it along the right path.
What's interesting is that Tolstoy shines up Kutuzov's reputation without trying to whitewash his flaws. We still see how old, out-of-shape, tired, and even lazy the man is. By showing us the human characteristics and the multi-dimensionality of these and other historical figures, Tolstoy takes the Manichean tendency out of history.
P.S. Manichaeism refers to any belief system that has a black-and-white, good-and-bad approach to morality, skipping over any nuance or gray areas.