I would keep him. I wasn't a fan initially, but given more matches, I genuinely think he has plenty to offer us. You mention needing an extra man along side him, but AM seems to like a back four with two "enforcers" in front of them. This leaves Chapman more room and time on the ball. Accepting this, it does mean only three attacking players, hence, in my opinion, the lack of goals, but when AM came everyone one new of his style at Mansfield, and said he would block up the backline and reduce the goals against. For the most part this has happened, not yesterday of course. So, Chapman fits AM's preferred playing style, so that's why he's central to the master plan, and therefore needs to stay. We have no-one else good enough to fill what AM sees as the pivotal role.