The defense was #9 in points allowed. I don't care how many yards the other team gets, if they don't cash in it means nothing. #6 in red zone TD defense. #7 in turnovers. They only blitzed 23% if the time and still got pressure on the QB.
There are things that need improvement but since it was the first year in this defensive system for so many players and only the 2nd year for the rest of them give Pettine a little slack. If the defense falls back next year cut him loose. If they take another step up the ladder then keep him.