There is no right answer to this. No good team can win with a bad coach (San Diego, Dallas, 2000 Commanders, etc.), but at the same time, a great coach can make an abismal team contenders (Miami). However, this is often the exception, not the rule.
People say Belicheat is great at what he does, but I say he couldn't have made the Lions win more than 4 or 5 games this season, just as Norv turner could have coached the Patriots last year to a 9-7 record.
An average coach can win with a great team. A great coach can win with an average team. A terrible coach will always make a great team lose, just as easily as a great coach can't win with a sorry team.