You can't compare one on one then to now because as I mentioned earlier, the rules were different. The game is geared to passing now.. The rules make it almost impossible to guard the receivers now. The rules now promote and more wide open, passing game.
In the last 9 games of the 1976 season the Steelers D gave up 28 points.. Yep, that's right.. 28 points in NINE GAMES.. Because of the rules now you'll never ever see that kind of D again.. The athletes are better now, faster and stronger.. But because of the rules the D's have no chance now to stop the passing game.. So you can't compare the passing of 15 years ago, to now..
You said the QB's and the DEFENSES are better now? I say nope, especially the defenses.. But IMO, neither are the QB's.. There are elites now, and the Brees's and Mannings and Rodgers would have been great 20 years ago too.. But the 2nd tier QB's would have struggled. They are having trouble now, they would be lost 20 years ago.