Agree about McCullum and think he is exceptionally good. Simpson also was probably exceptionally good. How many other cricket coaches/managers have been over past 40 years? The key indication is when much better results are achieved than expected, given quality of players, and the effect is...
Very interesting and complex question to debate. As usual it isn't decided one way or the other absolutely.
In cricket, the rise of the "Head Coach" as an influencer of team performance outcomes was resisted for longer than in football (notably by successful hierarchy-frowning Australian teams...