You are so much better a poster than this comment. I mean, really?
Do all these great coaches have losing records? Don't they play games to, y'know, win?
How good a coach is someone, if their teams don't win games? Competition in most leagues is that of "rough equivalents", teams with similar financial profiles, budgets, etc. That's why these lower leagues are consider breeding grounds.
And that is usually measured in terms of guys who teach people good defense is evidenced by the product they put on the floor. Similarly, people who teach good offense, or good big men, or good point guards, point to those players, those teams that they put on the floor.
Guys who are better teachers tend to win with limited resources. Those guys have winning teams.
Guys who are not the best teachers, tend to have losing teams because they don't communicate what it is they want effectively enough for the players to execute it. Talent is generally pretty even across lower leagues. You don't see a lot of physical specimens in these leagues.
If the talent is all in the B/C range, and not A, tactics, strategy, teaching - all of that stuff is amplified and takes on greater correlation to the team's overall success.
That's how I see it, anyway. Feel free to tell us why generally losing coaches may be good. Any year or two, sure I agree. But 6 or 7 years of consistent losing is not what I look for in a coach.