The scheme fit conversation in this thread highlights a common misperception about a rush backer in our defense...and I think, for some, it goes back to Dwight Freeney. Freeney wasn't a poor fit because he couldn't play in space, he fit poorly because he couldn't or wouldn't adapt to playing the run.
Playing in space accounts for such a small piece of the role that it wouldn't have hindered Freeney from finishing his career here. But...Freeney was a disaster against the run in 2012.
I wouldn't expect Barnett to ever rival Freeney as a pash rusher, but I think he'd bring solid pressure as a rusher and be assignment sound against the run.