I have some thoughts on Arians' offense and playcalling, but Leftwich is the playcaller now. And I think they'll tailor things to fit Brady's strengths and maximize the weapons they have. I don't think Brady is as dangerous a passer as he once was, but it was only a couple years ago that he threw for 500 yards in the Super Bowl.
Arians' calling plays for Ben and Luck (and even Jameis) -- who thrived in a downfield passing attack, who liked to hold on to the ball and shrug off tacklers -- probably doesn't have a whole lot of significance for the 2020 Bucs with Brady. Arians might be stubborn, but he's not stupid.