Montana won 2 Super Bowls before Jerry Rice ever entered the league. Then he won 2 more with him, and would have likely won more barring the injuries he sustained under the rules of the game that Brady has never had to endure.
Brady had Moss - every bit the impact player that Rice was - and did not win a Super Bowl with him. He's had one of the greatest tight ends there ever was. His offensive line has always been one of the best in the league, and crucially, he's had the greatest defensive coach of all time for his entire career until 2020. Brady has had everything he needed to win big throughout most of his career.
Here is Montana's Super Bowl Kill List: John Elway, Dan Marino, Boomer Esiason, Ken Anderson. All multi-time Pro-Bowlers, all won at least one M.V.P., 2 are Hall-of-Famers. 2 of those wins were blowouts (Brady has never led a Super Bowl win by those margins - not even close).
Here is Brady's: Kurt Warner, Jake Delhomme, Donovan McNabb, Russell Wilson, Matt Ryan, Jared Goff. 1 Hall-of-Famer, 3 good Q.B.'s, 2 lousy ones. Average margin of victory is less than a touchdown. Only 1 victory was by more than a touchdown, in a game in which the Patriots scored 13 points.
I'm fine with the argument that Brady is the greatest/most accomplished. You can't take away what he's done, and while a counter-argument is that he's been able to play longer than Montana, a great deal of that credit has to go to Brady for keeping himself fit enough to maintain his career for so long. But it's frankly silly to dismiss the argument for Montana as if it has no merit.