I don't have a problem with him getting 30 minutes like Bogi, but he isn't efficent or a good enough defender to make up for his lack of shooting. He had a solid game, but pretty much in line with expectations. 20 shots to 22 points isn't anything groundbreaking.
Fox needs to be surrounded with shooters, so his minutes need to match up with Belly as much as possible. If Belly continues to struggle, then sure, there's a point where Bagley's positives outweigh his lack of a shot.
I trust Joeger to know when they reach that point.