Neither one is an offensive creator at a high enough level for this team that is desperately trying to make the post season. They both can handle the ball and bring it up to start the offense, but that isn't enough to compete offensively, if playing together.
Keon has really earned a spot and identity as a 3&D guard, with his ability to shoot a high percentage and a relatively quick release. Carter, while already good defensively at this level, is neither a real 3 pt threat or a shot creator yet, so the team loses flow on that end. Doesn't mean he's not capable of improving those things, but that he hasn't proven it within the small window the team has had for him to work with.
All that's been said, I'm certainly rooting for him to expand and improve. Even if that means some more time in Stockton, where they can afford to hand him the keys and work on whatever he wants this season. I wouldn't look at it as a negative, but just part of the circumstances of this "red shirt season". It definitely worked for Keon,... no reason it can't work for Carter, regardless of whatever spot they were drafted or not drafted in