The Grizzlies, who virtually all NBA analysts had said are going to have a break-out season, are loaded with talented players. Their season has been horrible so far. Their former coach, Hubie Brown, was having health problems through the start of the season and recently retired. His replacement is a rookie. According to your theory, they should have just got it together on talent alone...
Plenty of coaches in NBA history have come close but failed at getting a championship. Did the existence of Michael Jordan prevent anyone but Phil Jackson from being considered a "good coach" for their 6 years? A lot more have never come close to championships at all. Saying Adelman is among the worst in the league is an exaggeration at best. Name the dozen or so coaches that are so much better than him?