I believe coaching plays a major role in all professional sports. MLB, perhaps, is the least important, as there are no real designed plays or strategy.
However, with football, basketball and hockey, coaching is very important. Theres a reason that Phil Jackson, Pat Riley, Pop, and Sloan are some of the winningest coaches. Obviously talent plays a large role as well, but if you put Leonard Hamilton, Isiah Thomas and Eddie Jordan on these teams, they would not do very well.
its easy to praise the players when a team is doing well. when they are doing bad, the coach takes much of the blame. Unlike a QB, a coach only gets the negative blame, rarely is praised for much publicly. But that doesnt' mean they aren't important and a team will go much further with a good coach than with a bad one.
Look at when Rudy T took over LAL for 1 season. Look at the Bulls when Skiles took over. Look at the Celtics when Rivers took over. Look at the Heat when Stan van Gundy took over. Look at the Knicks when Riley took over. Good coaches can improve good teams quickly and bad coaches can destroy good teams.