My point, which you didn't get and so I'll spell out in full, is that much like teams adjusting their playing styles to match whatever the most recent Cup winner did, coaching hires go in cycles and tend to chase after what someone else did. While you can list off 8 coaches who satisfied the criteria you lay out, I can name 6 others (Pat Burns, Peter Laviolette, Joel Quenneville, Claude Julien, Darryl Sutter, Barry Trotz) who won a cumulative 9 Cups who were previously NHL head coaches before the job where they won a Cup, without an AHL stop in between. Should a team wanting to have Stanley Cup hopes chase an AHL head coach, or a coach who just came off their NHL gig? Cause ... it's a pretty even split there.
Further, while Cooper, Bednar, Laviolette, Hartley and Tortorella (and Trotz) all won a Calder Cup before going on to win a Stanley Cup, presumably good coaches like Bruce Boudreau, Todd McLellan, Jeff Blashill and Willie Desjardins also won a Calder Cup and never got close to a Stanley Cup. [In the case of Blashill and Desjardins, never got close to getting close to it and each of them were hyped as up-and-coming smart coaches with bright futures as NHL head coaches.] Sheldon Keefe is TBD. What do we make of that?
Countless other coaches were promoted out of the AHL to be NHL head coaches and never had success. Do we ignore that for the 8 select success stories? And if so, can you or anyone else explain how we're supposed to know if Bannister or whoever else is going to be #9 in that select list, or part of the Boudreau / Blashill list, or part of the "oh yeah, they also came up and coached in the NHL ... and were pretty forgettable" list?
This is where I have an issue with some conclusions that get drawn. both in this forum and on this site and elsewhere. The fact that poor or inadequate decision making still leads to a great outcome doesn't somehow validate the decision making that took place.
How did we know before November 20, 2018 that Craig Berube was a good coach? We didn't. He got hired because we needed someone to take over short-term while we got to the offseason, where we'd presumably do the full-fledged search for the "right" coach. Looking at people's comments the last few years, one could put together a decent argument that Berube still isn't a "good" coach, he just happened to be in the right place at the right time and circumstances all came together in a magical way such that we won the Cup.