Fwiw, I don't think Kerrigan will ever be the 15-20 sack guy either but he has such a good all around game and to me the thing I notice is that he impacts games on a regular basis in a way that Rak doesn't. I think at this point it's fairly safe to say he's the best player in our front 7. All due respect to London, who's still playing at a very high level but he isn't what he was when he first got here.
I think at the end of the day our pressure problems are across the board. There isn't a single truly dominant pass rusher on the defense and while Kerrigan and Rak are very good there a secondary push up the middle is needed and sorely lacking. This team could use a true NT and another pass rusher in the worst way, even before Rak's injury. So you have lunch pale guys on the line, very solid but not overwhelming rushers from the LB spots to round out your personnel problems and you combine that with an unimaginative, predictable DC and Orakpo's injury and you wind up with what we currently are seeing. My main disagreement is that this was ever an elite group to begin with. They're certainly suffering from the injuries' they've sustained but I think the total impact is much less than many would have us believe and the D wouldn't be overwhelmingly better had they not happened.