Marsh is still in process of transition (at least mentally) from "baby brother/little brother" (see family pic from his recruitment) to biggest dude on the court. It's probably only been since he got to Wake that he's realized he is the biggest dude who can literally move almost anybody on the court whenever he wants to.
He's still figuring out when to do that, and how to do it (without getting fouls called on himself). As that process continues, I think he has more upside. He also seems to be limited by his stamina. Doesn't look like he can go effectively for long stretches. He needs rest more frequently than some of the other guys. As that improves, he will be a much more difficult matchup and make Wake a more effective team.