The offense is being run through the 5 players in bold. That isn't really possible unless you bring a couple of them off the bench. Corbin has done a good job of doing just that, while also using player combinations that make sense (Favors/Marvin, Kanter/Evans). This is exactly how you get a better idea of what you really have in all these young players. Further, Burks' minutes are going up overall, while RJ's are going down. Kanter was a complete mess to start the season. We'll see what happens to his minutes when he starts to play consistently well (against the Clips, Favors and Kanter got their first 4th quarter minutes together since Enes's last start).
I too think RJ is being relied on a bit much. He and Marvin have been very efficient scoring off-ball, but Alec is coming around as well. I think Alec will likely be getting 30+ minutes by the end of the season. Hard to say where Kanter will be.