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.
Faint praise. Brady has surpassed those other guys as a champion several times over. Lebron is the only valid comparison, and this assumes he wins more championships; I think he will. Wilt was probably the 3rd best player on that 1972 Laker championship; Jerry West and (iirc) Gail Goodrich were more valuable. Kareem took back seat to Magic for those Laker championships (and later to Worthy as well). Shaq was second fiddle to Wade in the Miami championship. And Peyton "wasn't that good" that year? What you mean is that he was terrible.
Yeah the more I thought about Wilt, the more I probably should have counted West as the best player on the Lakers team.
Shaq was the best player on the Heat (or at least the most important). They were 42-17 that year with Shaq and just 10-13 without him. And they fell off a cliff and won 15 games when Shaq left. He moved the needle, not Wade.
The 80 Lakers, Kareem was absolutely still the better player. They obviously don't win without Magic, but Kareem, the man who won League MVP that season, was absolutely the Lakers best player in 80. I don't think there is really an argument for Magic that season. Now starting in 82, Magic was probably the better player, but not in 80.
As for Peyton, he was bad, but I also don't think they win the Superbowl if they don't go back to him. So while Miller was probably the better player, I do think Manning was the most important player to them actually winning the Superbowl.