With the talent they have on defense they could be scary under him. He's not a media guy so he wouldn't get into Jerry's spotlight.
I think Aaron Glenn could be a great choice.
They should definitely bring in a defensive coach to toughen them up.
Facts.
Cowboys have always been at their best when they had a defensive-minded coach.
Tom Landry - DC of those great NY Giants teams back when Vincent Lombardi was the OC. Played DB at Texas and NFL
Jimmy Johnson - D-line coach at Oklahoma and DC at Arkansas before going to The U. Was a D-lineman for Arkansas in college.
Bill Parcells - DC in college and the NFL before becoming HC of the Giants. Was a LB in college before becoming a coach.
Their 3 best coaches in terms of creating a good culture...all defensive minded. The Cowboys with Landry invented the 4-3 defense used by damn near everyone as a base for decades.
Jerry loves offense but the Cowboys need defense as the focus. It's in their DNA. They're not much different from the Steelers/Ravens etc., except those teams embrace their DNA while Jerry chases dollars and media attention.