Silent G gets minutes at PG by default and JB doesn't trust him enough to give him minutes there unless its against weak competition or absolutely necessary e.g. Ennis foul trouble. And right now he doesn't seem to trust Buss enough to really give him any minutes there.
Over the last 5 games Ennis has played 37 or more minutes in 4 of 5 games and the 5th game was Bingo where he got himself into foul trouble and it happened to be a weak opponent so JB gave some other guys some run.
I would say that that suggests that Joseph will get first crack next season at being the backup point and will get whatever minutes are available there and they aren't likely to fall to G or Buss. I think Joseph will have the MCW freshman year role next season behind Ennis.
If Cooney continues his current developmental curve there should be somewhere between 10-15 minutes behind him for Bus and G to fight over. I don't think G will get any minutes at SF next season as we should have Roberson, McCullough and BJ eating those minutes. Very possible that BJ will take the minutes behind Cooney depending on his development. If Grant stays I think this result is more likely than if Grant were to leave. There will be a big playing time jam next season, it will be interesting to see how it resolves itself.