I think that that is a flawed analogy - the numbers that count in this instance are the percentage of students that a teacher is able to coach into successful careers. It's no surprise that Indiana has a lot of successful students, they have more than 4 times the number of students that Curtis or Rice or BU graduates. If you look at how many of them are now yoga teachers or business people you could build a case for any of these conservatories being great schools to learn not to do music also. The teachers who prepare a lot of their students for orchestral careers (i.e. Hal Robinson, Ed Barker, Paul Ellison, etc.) had orchestral careers that were very successful. They were also very good soloists, great chamber musicians, and very smart people.
To say that every high school basketball coach is equally valid disregards the fact that just like music, only a tiny fraction of high school b-ball players go on to play in college, and then even fewer go on to professional careers. I can probably predict that if Larry Bird started coaching at Central High School that a larger number of his kids would go on to college and professional careers.