If I was GM and somebody asked me what is more important a great QB or a great coach, I would say a great coach. Coaches are more important than people realize.
A team does not indeed ALWAYS need a great QB because at times you may have a great RB to cover up. If you were to have an amazing back, the QB could hand him the ball 90% of time. This means less time in the air where most quarterbacks are judged. If I was a GM I would draft/hire an elite quarterback.
A great coach is more important than a QB because they're the ones who make the hardest decisions. Coaches also are the ones who teach the team how to be successful individually and as a team. Think of it as this way; would you rather have a great team and a bad coach or a balanced team and a great coach?