If we are discussing this imaginary battle should we put into the formula that Lee was fighting a war during a turning point in modern wars? Lee had been trained in Napoleonic warfare but was fighting at a time when those tactics were for the most part obsolete. Very few men during the Civil War understood that and the war didn't change to meet the new technology until it was late in the war. So if the war had been fought in the 1840's instead of the 60's would the outcome have been much different? And if Lee had fought the war BEFORE the massive changes in rifled muskets, rifled cannons, rail roads, mass production etc., would Lee have been a BETTER general? Maybe a good enough general to be able to defeat or at the very least stalemate Napoleon?
Times were certainly changing -- but the Prussians were able to adapt to technology at this time, using techniques very similar to what Napoleon used. The French raised Napoleonic tactical methods as near to perfection as they could have been by the 1850s -- and beat the Austrians (the 2nd best army in Europe) at Solferino and Magenta in 1859. The Prussians spent the next few years beating everyone in sight (the Danes in the 1864 3rd Danish War, the Austrians in the 1866 Austro-Prussian War, and the French in the 1870 Franco-Prussian War) under the leadership of Helmuth von Moltke. The Prussians began adopting the breechloading "Needle Gun" in 1848 asnd switched to it completely before th 1864 war; the French switched to the much-better breechloading Chassepot rifle after the 1866 Austro-Prussian War; the Prussians swirtched completely to the quick-firing Krupp breechloading artillery before the Franco-Prussian War. The Prussians did so well this period and the decades that followed are known as the "Age of Moltke" to military historians.
Napoleon rose to fame in a similar period of wild change. The armies of Europe were all based on slavish emulation of what
supposedly caused the success of Frederick the Great from the War of the Austrian Succession (1740-48) and the Seven Years War (1756-1763). This led to small, slow-moving armies of professionals, with campaigns mostly about marches, counter-marches, shrewd maneuvering and few battles. Armies moved very slowly and rigidly, bound to masses of artillery and long, heavy. slow-moving supply trains (wagons). Intellectual ferment had begun in the French Army, however, with the new artillery system of de Gribeauval, new ideas about increased skirmishing (much of it returning from the defeat in Canada during the French and Indian War), and theories on how to restore quick movement and decisiveness to warfare.
When the French Revolution brought foreign armies to France to rescue the Royalist regime in 1793, desperation and necessity caused the French to merge their raw volunteers with their remaining professional units. Clouds of skirmishers now swarmed the battlefield; attacks in column became common, and only the professional units routinely fought in line. The Revolution mobilized the masses to fight (the
Levee en masse), raising the scale of war to a previously unimaginable level. Ill-disciplined French armies swarmed into other countries, changing everything.
Napoleon grabbed the reins of this chaos, co-opting both the professionals (like Berthier and Davout) as well as the raw recruits of society (Murat was studying to be a priest before he quit to join the cavalry; Massena was a supposed merchant and probable smuggler down in the Piedmont). For two decades he made war across Europe, rampaging over almost every nation and commander he faced. Finally, in 1813, his enemies figured out how to deal with him. With Napoleon facing the Prussians, Russians, Austrians and Swedes in Germany, they decided that whichever army faced a force commanded by Napoleon in person (no matter the odds) would fall back while the others all advanced. Even in 1814, Napoleon and his commanders often defeated their enemies when heavily outnumbered.
Clearly, Napoleon could adapt to changing conditions and triumph. I see no reason to believe he wouldn't have adapted to the technological changes of the Civil War. The tactical difficulties are no worse than the ones French soldiers had to deal with in the 1790s, and the operational and strategic principles Napoleon was a master of were all still the same.
Lee, OTOH, did a very good job of adapting to Civil War changes. He didn't lose his war because of rifled artillery or breechloaders or repeaters or railroads. Lee lost because he
was not quite good enough to beat a numerically superior foe with more resources
sufficiently to win the war. Napoleon
was good enough to pull that trick off; he did it
several times.
Tim