I think if you look under a microscope the d is performing good enough to win games.
but as a HC, McD is placing far too much trust in this battered defensive unit to get stops when it has proven time and again this season that it cannot get off the field. He needs to start being more aggressive on offensive and let that unit close games instead of trusting the defense.
in short, as a DC, McD is doing fine. As HC, I think he has done a pretty lousy job this year