It's not about the names on the roster, it's about the play on the ice. The coach controls that far more than the GM.
Yeah, but if you're a deeper, more talented team, you don't need as great of coaching to produce a like result on the ice. A star GM and a decent coach will find more sustainable success than a star coach with a decent GM. Hell a lot fo coaches who aren't very good fail because they don't have the perfect pieces to do what they want, a star GM could get those right pieces so that even a mediocre to bad coach wouldn't hold his team back.
For a control case of how effective a coach can be, look at Ottawa. Maclean has them playing great. Clouston had almost the same roster and the players said it was awful, and that reflected in the standings. So that's how impactful a coach can be.
Can someone present an example of a GM coming, changing a team but keeping the coach and having success? I can't think of one off the top of my head (maybe New York or Buffalo or Edmonton?) but I am curious and the lack of prominent examples doesn't mean a coach is more valuable.
Star GM for sure, even if the coach isn't that great, a star GM will will get you enough good players to be competitive.
Just because a team has good players doesn't mean they'll be competitive. This year alone there's a prime example in Buffalo. Well constructed team, some very talented players, but last place in the East. Now I'm not blaming Ruff for this, I have no idea why Buffalo is slumping and don't have the knowledge on them to guess why.
I'll take the star coach. Look what the Wild did in 2003 with a mediocre roster. Jacques Lemaire was a great coach while Doug Risebrough was a moron of a GM. As someone else mentioned Pheonix is a great example as well.
Having good players doesn't guarantee success but having a great coach will bring out every player's potential.