I never thought about this, but it puts those YouTube recut parodies where he's an evil megalomaniac in a new light!
However, remember that in "Yesterday's Enterprise," that AU Picard was still noble and heroic. And in "Tapestry" he's a 60-year-old dweeb, but still a totally nice dude.
It seems that Picard just varies a lot, under different circumstances. Given how restrained, controlled and deliberate his personality is, this makes sense. Jean-Luc Picard is a man who forces himself to act appropriately based on the principals he was raises with and the behavior his job calls for. The Picard raised on utopia Earth, and working in Starfleet, very deliberately acts out the principals of both. Is it any surprise that a Picard raised by Remans would act more Reman than Reman, or that a Picard raised on a fascist Earth would be the best damn fascist on the planet?
Compare to characters who wear their natural feelings, or lack of, on their sleeves. Data would likely be the same logical, socially clueless Android no matter what society he was brought up in. B'Elanna Torres would have volatile emotions and a talent for Engineering whether she's in Starfleet, the Maquis, the Mirror Universe, or a WWII French Resistance cell. But Jean-Luc Picard has tailored his mannerisms and reactions to his society. No surprise there are so many different Jean-Luc Picards in the multiverse.