This often comes up with my friends and I when we are watching a game. What do you think the most important position on the football field is during the game? I always say the coach because if they stink, the team will lack structure and motivation. Most of my buddies say it is the QB which I guess I can see where they are coming from with that answer too.
If you look at it, if you have a QB like ryan Leaf, Akili Smith, Rich Mier for examples you will never win anything. you will be lucky to be 8-8. they lose games for you.
I think all players are important. They all play a key role to help make the team succeed. However, I would say the Linebacker or Quarterback are the most important positions on a team, although you are right about the coach.