Very legit question.
We had a championship caliber defense.
Special teams was coming off a strong season, Carpenter had a great year.
It all depends on how we dealt with the offense during the offseason. McCoy likely would have happened regardless of the head coach, not sure who the QB would have been. We probably would have been much more competitive than we were with Rex, and I didn't really think Marrone was that good of a coach, but he was young and might have improved. We would not be in as bad a shape as we are now if he stayed.
So, Marrone leaving hurt, but the decision to hire Rex hurt much more.