Okay think about it this way, as Napoleon, as a way to justify his greatest mistake.
You're considering invading Russia, so you look at the two who came before you. The Mongols who utterly dominated the Russians, all be it, Russia wasn't centralised at all, so then you think: "Okay then, what else is there?". So you look at Charles XII's invasion of Russia while it was under the leadership of the one of the greatest Russian leaders, Tsar Peter the Great. Charles XII, barely a boy, won a plethora of battles during the invasion of Russia, and nearly brought them to their knees but ended up losing the war due to a lack of reinforcements and food which was also due to them being so far in Russian territory. So you think "what else is there to consider?", and you think of the Polish-Muscovite war of 1605 where the Poles took Moscow, but in the Russian's favour, they were also facing a succession crisis known as "The Time of Troubles", where Russia went through four Tsars in the span of the war. But even considering this, the war was still significant. If I was Napoleon, I'd think I'd be able to take Russia.
My point is, you're thinking that it was obvious that Napoleon would've lost but I don't think it would've been as obvious back then. Especially after you had just steamrolled the entirety of Europe, and set up many puppet governments, so you'd have access to some of their manpower. I actually don't know why I wrote out this paragraph, considering I don't actually think he's the best... but whatever. Who do you think is the best? Just curious.