I questioned the fit of Shazier in the first. I thought he got bounced around too easily and needed to be in a defense that protected him more. Now, he was lighter in college than he is now (put on 15 pounds for the combine). Then, the Steelers drafted Tuitt, who has good power and speed and plays as a legitimate 310 pound DL. Still, to me, not quite enough oomph in front of the smaller linebackers. McCullers changes that. According to Coach Mitchell, they want him to drop another 20 pounds and get to 330, that is still massive. They also added Philon (who is a legit 300 pounder) and Mauro (who they list at 282). When you have Williams and Arnfelt coming back, that is a host of big defensive linemen and gives some belief that they can keep this smaller LBs clean.
McCullers pops up off the snap, but he still is so big and strong he rarely gets pushed out and you cannot just leave him on a center because when he wants to, he pushes single guys around. The Steelers could be looking at 3 big, strong, DL and two quick guys on the edges. Hard to double them, even harder to slide guys to the next level.