I had a co worker whose son and daughter played AAU basketball when they were 14-15 and she got them both private coaching thinking they would get a college scholarship. The daughter did get a partial scholarship but it was for volleyball.
My cousin had a daughter that was big into swimming and had a private coach during for about 5 years. She would practice an hour before school and 2 hours after school. A lot more during the summer. She did win the state high school championship in a couple events. She did get a scholarship to an excellent school and is now a doctor. I mentioned to my cousin how great it was that she got a scholarship and they replied that what they spent regarding swimming (travel, pool fees, private coaching, etc.) would have paid for her college.
Point being (which is what you were alluding to) is that most elite athletes improve mostly by going to various camps and private coaching and working hard on their on.
Sure, at this level, all top flight players do a lot of work on their own and many have own strength and conditioning coaches and skill coaches.
But here is the question-- if a certain coach should not be given credit for player development, then why is that same coach, by the same people making the first attribution, also being held responsible for other players
not developing?
I know this from son's and daughters collegiate soccer careers. The amount of time a coach has to work with a player on skill development is relatively small as much of the season is devoted to tactical matters. It is hard for athletes to find much time in the season, for example, for strength and conditioning. They are more in a maintenance mode and the improvements come in the off season and then NCAA rules limit how much time they can have with coaches. In the off season, so-call "captains' practices", which are largely athlete directed are a big of the off season process.
But, coaches push athletes to develop certain skills and learn to play in ways that might not otherwise due, as well as identifying flaws in their game that have gone unnoticed. From there, it is up to the athlete to make the requisite changes.
There is also the learning the tactical/mental side of the game. In the soccer world, this would mean becoming better at field positioning, learning when to make certain kinds of runs at certain times, subtleties about defending as a team and each persons role in the formation and so on. B-ball has the same dynamics.