See, I think this analysis is self contradictory. When Capers arrived, he had a great run defense and that was where the emphasis was. He had to scheme and get nuts with fronts and blitzes to get pressure. The only year they both worked in concert was 2010, not surprisingly.
Since then, the pass rush has been middling and trending down. But unlike 2009, so is the run D. Peppers has helped the pass D, but it hasn't been consistent enough to stop opposing O's.