The numbers are just about Equal when you compare the Niner and Pats' dynasties. However the conditions under which they competed were very different. I have always believed that one of the big pluses for Brady in the Brady/Montana discussion, was that Montana essentially had all his vast success with essentially the SAME roster, while Brady has taken essentially 3 different teams to his 6 superbowls. Now THAT is an accomplishment that is unparalleled...at least in my humble opinion
Yes, the eras they played in are quite different. It's tough to compare. Each quarterback has had advantages (and disadvantages). I'm going to try to be as objective as possible here when looking at these two, so here it goes.
1. Passing numbers are hard to compare. When Joe Montana played, a passer rating of 100.0+ was basically unheard of it. It rarely, if ever, happened in regular seasons. This season, Russell Wilson, Kirk Cousins, Tyrod Taylor, and Cam Newton all eclipsed ratings of 100+ (okay, Taylor/Newton were at 99.4 -- close enough). All of those guys are pretty mediocre passers. Passing numbers are really hard to compare.... the ref has really clamped down on illegal contact, etc, which has allowed receivers to run rampant.
Matt Ryan had a QB rating of 89.0... that was 20th (!) in the NFL. 19 players had a passer rating over 90, including 6 over 100. In 1985, 89.0 would've been 4th-best in the league; 3 QBs had a rating over 90. None of them had a rating over 100.
Montana has a career passer rating of 92.3, including 95.6 in the playoffs (127.8 rating in 4 Super Bowls, including 11 TD and 0 INT). Brady is at 96.4 in the regular season, and 89.6. Objectively, I think Montana's numbers were better. Montana putting up passer ratings like that in the 80's are more impressive than Brady's in the modern day NFL. (Again, look at the numbers guys like Cousins, Taylor, Newton, et al. are putting up.)
---
2. Longevity is hard to compare. Again, this one is tricky. Another advantage that Brady has is that the game has become so ****ified. Quarterbacks are absolutely coddled these days. The league has dramatically cut down on hits to the quarterback, defenseless receivers, etc...
Brady has said that he plans to play until he's what, 45 years old? Part of the reason that's possible is because Tom keeps his body in pristine shape, but part of it is the fact that he's just not subjected to the hits that quarterbacks used to be. Again, this is not taking anything away from Tom... I'm just saying that there are two parts to the equation (Tom is fulfilling his end of the bargain [keeping himself in shape], but it also helps that the league has toned down on viscous hits).
Montana played 13 seasons.... Tom could potentially play, what, 20 seasons!? It's hard for me to believe that Brady could have remained as healthy in the 80s as he has in his career.
...
3. Salary cap era complicates things. Montana got to play most of his career without a salary cap. The 49ers were absolutely loaded, and frequently wildly outspent their opposition. The teams Montana played on definitely had more talent than the ones Tom has played on.
Parity in the modern day NFL is ridiculous. The fact that the Patriots practically a lock for the AFCCG every year is absolutely stunning. This one is a huge advantage in Brady's favor.
...
4. Brady had more success. One of the dumbest criticisms of Brady I see is that he's lost two Super Bowls. Who cares? Losing in the Super Bowl shouldn't be viewed as any worse than losing earlier in the playoffs or missing it at all.
Brady could very well win his fifth this year, and have reached the Super Bowl an astonishing 7th time. The sustained success just blows my mind.
------
Ultimately, I think Montana and Brady are tied right now. I think it's a coin clip, and I think compelling arguments can be made for either player. If Brady wins his 5th this year, I think it's case-closed. At that point, he's indisputably the best in my book.