Barkley is going to be tough for this defense. Every team knows that the Cowboys aren't able to defend the run consistently.
I don't think Zimmer has a grip on his personnel yet to be able to run his defense the way he wants. He doesn't yet know the individual strengths and weaknesses of his players so that he can scheme accordingly.
IF the Cowboys expect to win, Cooper Rush has to keep their offense off the field. He has to avoid three-and-outs, and has to be consistent in working the clock.
It is a tall order.
But two of the three interceptions he threw against the Eagles last time were actually on Michael Gallup; he wasn't fighting for the pass like he should have been, presumably still tentative from his injury. He let the defenders move past him to the ball, and should have been benched.
But Rush gives the Cowboys a chance they wouldn't have with Dak in that he sees the field better and doesn't have to count on CeeDee or Ferguson on every pass play.