How does the offense sustaining drives have anything to do with the defense?
Yes, the defense needs to get off the field one way or another to get the offense on, but what does that have anything to do with what the offense does once they take the field?
Also, the Packers defense was 11th in points and yards allowed, 7th in takeaways, and the team was 14th in time of possession. So I don't agree with your theory at all. The offense struggled on their own this year, it had nothing to do with the defense.
Everyone remembers the 49er game because it's fresh in their minds, but overall I think most of us would agree that if we would have been told before last season that we'd be 11th in points and yards allowed defensively, we would've been very happy with that and figure that would be enough for us to be a dominant team.