There are only a handful of players in any professional sport that have won titles as even arguably the best (or most important) player for at least two different franchises.
Tom Brady and Lebron James are the obvious 2, but there aren't any clear cut for sure thing others.
In basketball, Wilt, Kareem, Shaq, and Kawhi all arguably fit that mold (clearly the best player for 1 franchise, but arguable for the other). I'd probably count the first 3, but would still rate Duncan as better (and certainly more important) than Kawhi, despite Kawhi winning Finals MVP that season for the Spurs (Parker was also arguably better as well).
In football, arguably you also have Peyton though he was basically benched in Denver before retaking the starting job and winning the title that year. I'd probably count Peyton, though Von Miller was certainly a monster on defense and Peyton quite simply wasn't that good that year.
The only person you could argue in the NHL is Patrick Roy who won 2 titles with Montreal and 2 titles with Colorado, and since the goaltender is so important, I think I'd count him (though Sakic and Forsberg were both great players in Colorado). The best position player to win with 2 franchises is Messier, but there isn't an argument at all that he was better than Gretzky in Edmonton.
All of the great MLB players have all basically only won titles with 1 franchise.
So in the history of the four major professional sports, Tom Brady has now joined Lebron James, Wilt Chamberlain, Kareem Abdul-Jabbar, Shaquille O'Neal, Patrick Roy, and Peyton Manning as the best and/or most important player on a title winning team for 2 different franchises. Pretty good company to be in.