I dont think an overconfident Stalin is in character. The guy was anything but. Pre-Stalingrad he was pretty much terrified of Hitler. Unlike Hitler, he never gambled until the deck was OVERWHELMINGLY in his favor.
If you are referring to my post above, I agree with your view in general - Stalin's basic setting was being careful, he only ever went "all in" if everything appeared to be in his favor. But if his plans seem to be succeeding all around and the Soviet military seems to be getting only easy victories over the USSR's smaller neighbours, I think some degree of comparative overconfidence would be to be expected, that is in comparison to the realistic capabilities of the Red Army as they would be without the Winter War in 1940. It is another question how this would manifest.