There are a few things.
I think the secondary has proven itself enough in coverage where Dom has more confidence in leaving them without help allowing for more attention to the run defense.
I think the Dline has been getting better, and Dom has learned more how the different players work best with each other.
I think having Neal/Perry on the field rather than Jones makes the entire defense better.
And I think Matthews could be very good at ILB if he would stay there. It was to easy for offenses to scheme to take Clay out of a good portion of plays by running away from him, or chip blocking or lining up where he would have to drop into coverage. In the middle, he has more chance of being involved in every play.
The world needs ditch diggers too Danny!!!