“Were it not for ten miles of salt water....”
.
You seem to forget the Russian winter.
As in WWII, had the continental tyrant been able to eliminate all opposition on the western front before turning to the eastern front, things might have turned out very differently.
It is generally accepted among historians that the British were the most effective opponents of Napoleon, that indeed the Continental System he attempted to force on his “allies” was the main cause of the war with Russia.