Tom Brady dragged the 31st and 30th ranked defenses in the league by DVOA to minutes away from a Super Bowl title in 2011 and 2017.
It's a very simple equation, Wozzy. Offensive EPA/Play has correlated to winning and postseason success more than defensive EPA/Play the last 15 years. Defensive performance is way more high variance year to year than offensive performance, as offensive performance is more reliant on the play of a single player (the Quarterback), and that's more stable year to year than the sum of the quality of play from multiple defensive players. So you have one single position who not only impacts his side of the ball disproportionately in relation to any other, he also impacts the side of the ball whose play, of late, has corresponded more to actual team sucess than the other.
It's not the ONLY thing that matters, but it matters so much more than absolutely everything else, and as of late it MATTERS MORE INDIVIDUALLY THAN THE WHOLE OF DEFENSIVE PERFORMANCE that it is absolutely the most certain indicator of contending for a title. No matter how many Breeses and Marinos you throw at us, those are exceptions and not the rule (not to mention, most of the years those guys didn't win a Super Bowl, another elite QB of their level or beyond ended up hoisting the Lombardi).
The best defense in the league last year was San Francisco's, how did they look after losing their third string QB who was performing well?