The defense was responsible for stopping the run. They didn't do that. They couldn't even stop the run when they knew the Bills just wanted to run out the clock. The knew the run was coming, but they couldn't stop it, and they allowed first down after first down after that. So, no, Dak wasn't responsible for the defense's poor play.
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As you pointed out, Dak was responsible for his own bad play when we actually did have the ball. My response to that is: Duh. That's not the point. The point is this is a team loss, and the defense is just as responsible for it as the offense, and Dak. This isn't all on Dak's head. It's partly on Dak's head, ya know, the part where he was actually playing on the field. He's not responsible for tackling the other team's running back.