I agree with this a lot. There can be 2 things at play here, you know. I think he was going old-school and carrying on the "you earn your minutes" concept. But I also think that is generally what is accepted as "player development", limit their minutes, coach them in between plays, etc., and Sloan did both to a fault. Sloan was rigid in many ways, and for a lot of it, that is why he was successful as a coach, his teams were disciplined and played the way he wanted them to. But it also cost him games at times, being too rigid to adjust to the situation. For D Will it is hard to say what would have been different to have been under a different coach at the beginning, but who knows, he may have blossomed even more than he did in his rookie year, Mitchell-style.
But my larger point stands, that there is no one single way to develop a player, there are myriad ways to go about it. And it is tough to say which approach is the "right" one as really it will depend heavily on the player themselves.
That said, imagine having CP3 under Sloan, being held back like that, limited time, chewed out between plays, the Sloan way. He would have been demanding a trade before the ASG his rookie year. lol