For what its worth I think you are absolutely correct in the fact that the quality of experts in any niche area of expertise varies greatly. Sport coaches are also notorious for odd and quirky methodology, and more often than not their methodology is based on experience and belief rather than some extensive scientific research.
Even if we would ignore methodology we could still stay that getting players to buy in and motivating them to work on the craft alone is something that some people are just much better at than others. Plus it wasnt too long ago, when these NBA shooting coaches were often trying to force everyones shooting form towards one perfect mold, until guys like Steph made them realize that natural form is a thing.
