You can make an argument for one season or maybe two, but when a quarterback has 7 Super Bowl wins, there is no way you can write off most of them, much less all 7, as "it wasn't him."
After 7 Super Bowl wins, it was Brady.
After 3 Super Bowl wins in 7 years, it was Mahomes.
Break the argument down game-by-game all you want, but after 10 Super Bowl wins, there is no dismissing Brady or Mahommes, at least not without showing desperation for trying to excuse-away why the Cowboys have failed for 29 years.