To me Garrett is a no-value add in terms of providing anything tangible on the field, he is just along for the ride.
Garrett is not exactly a bad head coach, he's just not a good one, he just seems to be there, not really doing much of anything. With that said, he deserves to be fired for this travesty, although he won't because the front office will want to give Romo another chance for a year or two before he's done and they probably think there's no point to starting over with a new head coach just yet.