It’s hardly rare for QBs to thrive on their second team. Even if you want to discount the Drew Brees situation, guys like Alex Smith, Kirk Cousins, Jared Goff, Geno Smith and Baker Mayfield have thrived in second (or third) acts.
teams prefer to use their own guy, and once you get the stink of being on a bad team it can be tough to get that off you. But development is not linear and is absolutely affected by surroundings. Most guys just aren’t great QBs on their own volition.