It was nice to find your intelligent and insightful post when I woke up this morning. I can imagine a boxing coach. He's trained maybe a hundred fighters. After scores get the crap beat out of them to the point where they quit because they can't take the punishment or injured, there is this one, the luck of the draw, that the coach can point to: "Look, he made regional golden gloves. I can do this for you, too." Yeah. This one particular boxer had the heart to figure it out for himself. Succeed or die trying. And he succeeded. No thanks to his coach. 90%? How 'bout 97+% is my uneducated guess. In my post, "The Best Advice You're Ever Likely To Get" I give you 5 points you must consistently perfect. You don't need a coach to teach you this. You can teach yourself. For instance, the #1 necessity is a perfectly straight stroke. If you can do all 5 requirement listed you will have a perfectly straight stroke. You can't not have a perfectly straight stroke. There are perhaps finer points to accomplish these to make it easier, but you've got eyes. Use them. All the goals and requisites are listed in that short post. You don't need someone to hold your hand.I don't think that's true. It seems like in the examples you gave (NFL, NBA, etc), most coaching staff had previously played at a very high level. Coaches like Popovich that never played beyond an HS level are very much the exception rather than the rule.
The issue is that in a niche sport like pool, you have too many buffoons that both can't play and can't coach. At least with mainstream sports, you have a long and verifiable history to validate someone's coaching abilities. In pool, you have either A) coaches that have played at a high level B) coaches with a long and verifiable history of success with coaching or C) coaches that just say generic shit like "I've been coaching for over 20 years, trust me". I'll let you guess which bucket 90% of coaches in the US fall into