The reality is that how good your offense is, compared to your defense, it's mostly due to how much money you're willing to pay out to make it happen. A team with a great offense rarely has better than a mediocre defense, because they spend more on shoring up the offense.
As for the game itself, over the last 20 years, the league itself has constantly changed the rules to make it easier for teams to put points on the board. It's what everyone should suspect. When you compare it to the game I first followed, where a QB threw the ball less than 15 times a game, and in a lot of cases, around 10.
These changes have happened to get more people watching the game. The old one score wins games of the past no longer apply to today's game.