RR is a very competent defensive coach.
Absolutely he is. Questions about his ability to be a top-notch head coach are extremely valid, but Rivera has proven long-term has is a very good defensive mind (without all the non-sense guys like the Ryan brothers, Gregg Williams, etc. bring).
I think owners like JR typically gravitate towards defensive minded guys bc they are typically more problem-solving oriented (i.e. how to stop offenses when all the rules favor offense). As part of that though, defensive coaches instinctively are more inclined to view situational football in terms of risk-mitigation versus offensive guys. Which manifests itself as being more conservative.
Both styles can be effective, but both styles have their limitations. I truly believe the Panthers could have won more games in 2011 (and 2012 to a lesser extent) had Rivera reigned Chud in more on some of the high-risk plays on 3rd and short. Conversely, though, Chud's offense was surely a hell of a lot more interesting than the Shula show.
Personally, I think a lot of the reason Rivera promoted Shula instead of hiring an outside coach was so that Rivera could exert more influence over play-calling. And that style worked last year with a dominant defense, and hasn't with a mediocre defense.
That does smack of a failure of Rivera as a head coach, though. Great HC's are willing to cede control to an innovative coordinator for the betterment of the team.
John Fox had an issue with that as well. Jeff Davidson?? John Fox doesn't have that issue now bc he has Manning, but that was certainly one of his failures as well.