You can't make fair comparisons because the nature of the game, and the rules, have changed since guys like Unitas and Starr were playing.
Let's face it, a 7 yard dump to Welker, which gets turned into a 25 yard gain due to Welker's special skills, is different than hitting Raymond Berry or Boyd Dowler 40 yards downfield on a post pattern with Bob Lily breathing down your neck. Which is nothing against Brady's ability to throw the long ball, but in the old days the long ball was the primary passing weapon. It's why you see low QB ratings when you retro-apply the formula to the old guard.
Montana benefitted from Walsh's innovative "West Coast" offense.
In the old days you could jam a WR all the way downfield until the ball was in flight, too. Receivers have an easier time getting open today. Even with nickel and dime defensive packages. In the old days the tight end was a lead footed moose used primarily as a blocker, and a dump-off guy. Downfield threats like John Mackey were rare. Today's tight ends can run 4.6 40s, block like a guard, and break tackles like Jim Brown.
Hell, the debate over whether TB or P. Manning is the best of this era isn't even settled yet. In most areas of the country, at least.
