How developed their bodies are or who played in the starting lineup is completely irrelevant if you're trying to develop young talent for the future. Kanter still has trouble executing simple team offense and defense. Giving him an opportunity to work on these basics in lower leverage situations against weaker competition is probably more effective than throwing him into the deep end. The same goes for Burks, although to a lesser extent. Regardless, Ty did a pretty good job bringing Alec along, and helping him develop into a better team offensive player. If the goal is giving young players situations in which to succeed AND spread their wings (i.e. get touches), and bringing them off the bench provides the best opportunity to do so, it should make absolutely no difference who starts in their stead.
FWIW, Burks and Kanter each played over 2000 minutes last season. They ranked 94th and 106th in the NBA, respectively. The Jazz had 5 23-and-under players average 10+ field goal attempts per game, which is virtually unprecedented. All of these facts attest to Corbin's commitment to development, despite what the ignorant masses on Jazzfanz think.