Just because Luke hasn't had killer stats doesn't mean he's not the MVP of this defense. Kuechly literally took a bottom-feeder defense and made it a Top 10 one last year. I shudder to think what would happen if we lost Keek for the season.
I'm not saying that Mitchell is the best player on the defense, not by a long shot. Kuechly is our defense. But, I'm saying that Mitchell brought with him an attitude that has spread to all of the other players. A nastiness. Anger. These guys are playing to hit somebody, and that started when Mitchell was injected into the defensive lineup.