That has been proven wrong so many times, its not even funny.
In any given season, a team can win big with a dominant defense and a so-so offense. (Ravens)
The reverse is also true. A team can win with a dominant Offense and a so-so defense. (Rams)
But to win consistently, the best way is to have a premier QB (Brady, Manning, Montana) along with a good O-line, running game and a strong defense.
We don't have any of those things right now.