I'm certainly not saying that Ayton is free from responsibility from his own lack of performance... you are imputing that.
I am saying that after five full seasons in the league with the same team and (mostly) the same coaches, if he is still not responding to their coaching, there is something fundamentally wrong with the coaching approach. At every level of coaching that I am aware of, if you have a player who isn't responding to the coach, the coach has a responsibility for the good of the team to either A) change how that player is being taught, B) discipline that player until they "get it," or C) failing all of that, remove that player from the team.
I (and you, and everyone else on this forum) are of course not privy to whether the Suns have ever attempted the first course of action. It certainly doesn't seem they have really ever done much of the second either. And the third remains to be seen... possibly this off season.
In any case, there is plenty of other evidence besides the case of Ayton that the coaching staff isn't great at imparting or managing other fundamentals for the team as a whole... team rebounding and elements of defense certainly jump out as particular examples. The Suns have had the advantage of great individual talent these last few years that has help obviate those shortcoming to get them to a certain point of success.