Staley's ability to use cover-4, cover-2 cover-6 and even cover-3 with a late movement of safety into the box was predicated on DL playing gap-and-a-half football to plug up the run without a box defender at snap. It does seem like we've lost a bit of our ability to do that with the loss of Brockers, Ebukam and Fox. Mostly Brockers. Think we took a calculated risk letting him go due to salary cap restraint and A'Shawn just has not been able to provide the same toolset.
Look at Staley's unit and Fangio's unit right now, you definitely need to horse to make it go. We had a lot of role players that we lost on defense since last year and their loss collectively adds up.
(Also, we were crazy healthy on D last year.)