Completely reasonable to want him as fresh as possible when they have tired themselves out and are allowing us more possession, but just the prospect of MB making a sub after half an hour, assuming we have seen off that intense start, isn't very likely. And there's the fact that he's the one player likely to take a shot, let alone put it on target.
Giving him that free-role behind Kent and another, finding space to get on the ball and without the defensive responsibilities that he's not so good at, feels sensible.