Banks is playing pretty well to be sure. But I am not sure it is a good idea to interpret this as Jaric is incompetent.
Jaric was one of the more effective players for a bad team, before the banks trade. Since the trade though the play at the other nonRicky positions (2, and 5) are not any better. In particular, Minnesota has crap for centers. When your 5 position can only manage 4 rebounds against the suns for the entire game, something is really wrong.
Bottom line is that Banks or Jaric, the team is still losing so Jaric was not the problem. Also it might make sense to play a lot of minutes with Banks as long as Ricky D is on the floor. At least he and Banks have played a lot of the season together and would not be on totally different pages.