Absolutely, the Cowboys aren't improving on Defense at all under Marinelli. Why, just look at how they didn't have a top ten defense in the league last year, something that allowed them to win over half the games they won when the offense struggled.
It should be obvious to anybody with real football acumen that Marinelli is the only reason this unit isn't #1 in the league last year.
Once again, where was the Defense against the Rams during the most important game of the season? No halftime adjustments. Nada.
The D disappeared during the playoffs this past year in 2018, back in the playoff game loss against the Packers in 2016 and once again during the playoff loss at the Packers in 2014. All under the helm of Marinelli.
You like that Marinelli playoffs record for the Cowboys?
Romo and Dak carried those playoff teams during those playoffs, NOT MARINELLI'S DEFENSES. FACT!