Sarky is not my favorite coach, but in fairness, his offensive output wasn't bad this year. Atlanta got killed mostly due to a depleted defense that had many guys injured. Sure, Sarky made some really bonehead calls, but his overall offense's output was good...far better than you would expect for a team that didn't manage to win half of its games.
Quinn is not that good as a HC. The idea that he will replace all 3 coordinators and call the plays himself strikes me as unrealistic. If he wasn't good enough to manage his 3 coordinators, how is he going to call the plays and manage the D and ST coordinators?