Coaches who can adjust to adverse conditions, be it player drops, QB injuries, bad tackling, are the ones coaching in the playoffs this year, with the exception of the NFL East, of course, which is a mess. You don't continually have an injured QB throw the ball, you don't continue to have your RB run up the middle with 9 man fronts hoping the other team won't catch on. If I can sit at home and call the play before it even begins, that's on coaching.
Take that fourth and goal, you beef up the line, you don't defend it with huge gaps that a washing machine can walk through. That's on coaching. When you blitz a handful of times with a throwing QB who has no receivers, or you play off no name receivers like they have super powers, you are going to lose. So even if Dak completed the touchdown passes he missed, what makes David Helman think the defensive coaching would've held up? That fourth and goal play was egregious!
It's really not even arguable anymore, Jason Garrett is like a bad bad conductor of a great of orchestra. JG couldn't adjust his suit pants if they were draped around his ankle. Marinelli, like a fine wine, went stale this year, and Richard has probably checked out knowing his job is lost.
I have to go with Bill B on this one: great talent cannot overcome bad coaching! And that's Dallas to a tee. (But we know who the architects of this disaster really are, JJ, & SONS)