Should Napoleon’s and Hitler’s invasions of Russia really be considered similar

[The Mikado]

Tsar Alexander I was by no means a genius, but he WAS someone who was able to learn lessons from past mistakes, and one of the big lessons he learned from Austerlitz etc was "whatever you do, don't let Napoleon destroy your entire army in one of his big flashy setpiece battle victories." The Russian Army getting away at Borodino rather than obligingly staying put to get demolished is basically the moment Napoleon lost the campaign. I agree with Cassius on that point: Napoleon had been counting on a decisive victory in which he utterly demolishes an enemy's main fighting force and forces them to the bargaining table to be wrecked prior to repeating the same thing two years later in another Coalition war, which was basically his MO up until this point. Alexander's stubborn knowledge that as long as a Russian army was in the field, Napoleon would have to account for it and could never really achieve victory is the biggest reason why Napoleon doesn't win the Russian campaign by simply destroying the Russian armed resistance, which he had every reason to expect he could do. It's what he did at Austerlitz, it's what he did at Jena.

[The Mikado]

Also, as far as I understand, while Hitler never thought the alliance would last, it seems like Stalin fully bought into it, to the point of dismissing the obvious signs that Germany was getting ready to attack.

Specifically, Stalin never thought Hitler would attack while Germany was still at war with Britain.

The fact that tiny Finland had fought the Soviet Union to a standstill the year before also did wonders in making the Germans think that the USSR was a paper tiger militarily, notwithstanding the VAST differences in types of war.