So that means the first 1/3 of Brady's career was played against these D's. I'd argue that since 2006, Seattle had the best D in '13 and '14 and TB beat them. TB as a rookie beat Oakland and Pittsburgh and the Rams (O first but still a solid D). TB beat Pitt, Tenn, Philly, NYJ, and Baltimore in the playoffs when they featured some tough D's. A 1/3 of Brady's career is about 2/5's of Montana's career. SD, Buffalo, Miami had lame D's. Cincy was not any dynastic D either.
You play who is in front of you. TB has played longer, won more, won at a higher %, and produced more offense per game, and he's a bad weather QB (greatest cold weather QB of all time) and two other teams in his conference have crap weather and Montana was a good weather (fog and rain sometmes) in a decent weather Division.