Buying ... carefully. The defense showed that it can play man on the corners, but struggled middle of the field after Shazier went down. Bostic, Edmunds and Allen improve middle-of-the-field pass defense. Seriously, does anybody remember Mitchell breaking up a single pass? Or getting to the receiver right when the ball arrived, not after?
Further, slash makes a solid point about Samuels being a legit 3rd down back when Bell needs a break. Dude played fullback, is a hell of a receiver, and averaged 6 yards per carry. Very good skill set for a 3rd down back.
As others have noted, health is a big, big factor. If the OL can stay healthy and protect Ben, the 2018 Steelers could be damn good - again.