You really believe that? I guess my experience is with club soccer as opposed to AAU basketball, but as both a former varsity coach with 20 years of experience at that level, I can tell you hands down that at least in terms of soccer, high level clubs have far superior credentials, methodology, and ideology then high school coaches.
That's not to say that there aren't good high school coaches out there, or bad club coaches. Part of being a good coach, IMO revolves around the opportunities to continue to develop as a coach as well as the educational made available. Not a shot at Varsity sports at all, but how difficult is it to attain a coaching authorization (for someone who works outside the school system) in the state of Iowa and then once its acquired there is very little required obligations to get it renewed. In addition to that the authorization isn't even sport specific. Outside the varsity level there are a magnitude of different levels of licensing one can attain to continue to move up the ranks, and those opportunities are not for everyone, and are difficult to progress through.
I was a successful high school coach with multiple state appearances and a number of conference championships, but but I found that there was very little out there in terms of resources or opportunities to improve my craft. The amount of resources and licensing opportunities available to me at the club level is exponentially greater than anything that was made available to me through the IAHSAA, NFHS, or IAHSSCA.
As someone who left the varsity level for the club/academy experience I think both are fantastic options. However, at the same time I think there are a lot of "great" coaches at the high school level, who owe their success, in large part, to the club/AAU system and the number of athletes who participate in club/AAU sports.