A much better measure is DVOA, which factors in opponents and a whole bunch of other relevant factors like turnovers ( http://www.footballoutsiders.com/stats/teamdef ).
2017: 16th (he took over a D that was 27th in the league the year before; that was Ryan's D)
2016: 10th
2015: 2nd
2014: 15th
2013: 3rd
2012: 11th
2011: 32nd
2010: 11th (Philly)
2009: 3rd (Philly)
All in all, his record is quite good. In 9 seasons, he has finished in the top half eight times, in the top 11 six times, and the top 3 three times. He had one disaster season - his first year in Carolina.
Incidentally, your 2011 stats are wrong. Carolina's D was 27th in points allowed and 28th in yards allowed. https://www.pro-football-reference.com/teams/car/2011.htm