You need elite talent to be a championship contender, this is absolutely true. It's also absolutely true that because everyone knows that, by the time you're deep into the playoffs you're generally facing teams which all have elite talent on them. At that point, having a coach who is smart and pro-active can win you a game or two, and in a close playoff series that can be the difference.
Coaching is not the most important thing, but it's still important.