Disagreed. Look at what the Steelers defense has done in the past with freaking Duck Hodges as QB. Look at what the Ravens D has done this year in many games without any appreciable offensive output. Great defenses stone the other team when the offense is struggling. Good defenses can be counted on to make a crucial stop or two when they have to. What defense did we have when we needed the big stop this week? I'm not saying our defense has been garbage this year, but they are wildly inconsistent, and can be soft as a marshmallow, which just won't do.
The Ravens have been below average on both sides. 17th offense and 19th defense.
The Steelers holding it together for a few games or so with a backup is a different story and either way outliers don't disprove the rule.
Not saying it never happens but most of the time and over a whole season both sides rely on each other.