I think we can afford to lose both Mackenzie & Brown. The game particularly our defence system has moved past that kind of one on one defender. We require pressure across the ground otherwise we are going to be cut up anyway. Having a great one on one defender if they are moving the ball cleanly wont do much.
The best thing is to have a couple of good marking talls who can read the play and play in the web like Barrass & Gov do. With Schofield as the optional defender based on height, or Gov forward.
I would prefer to get Mackenzie back to his old self and take Schofields role but we dont know that will happen and his kicking has always been suspect. I much prefer this fast thinking fast moving backline that backs in their kicking. McGovern, Hurn, Barrass, Shep and despite the odd brain fade Wellingham.