They're probably about average at development. Three (Tatum, Brown, Smart) of the recent successes are lottery picks. Some credit should definitely be given for the development of Rob Williams.
It does seem like they've had a harder time doing it when in contending mode. The early Brad years it seemed like it was a real strength. Olynyk, Smart, and Rozier showed growth, and even what they were doing with guys like IT, Turner, and Crowder. Brad was very good at getting improvement out of his players.
Since going all in for Kyrie and Hayward, it hasn't felt the same. Culminating with the current situation with Langford and Nesmith, hoping we didn't bust on consecutive #14 picks, and having little depth to show from the later pick try outs we've had over the past few years. Grant Williams and Pritchard do offer something there. But it's unfortunate to have nothing to show out of Edwards, Fall, Waters, Green, Yabu, and Zizic. Guys they invested some sort of money, draft capital, or playing time in and never really contributed.