I am not as worried about this as the wingers and Centers actually working together for defence.Mamaulo tries hard but lacks the essential ingredient which is pace. I don't view him as a Sheens style winger. We know with Fifita how Sheens deals with loose units so if Nofoaluma is not on his game I'm sure there will be consequences.
Sheens could put Beau Ryan in position to score (ok he had some pace).
As long as Mamaulo can defend, we can plug that gap on the wing. It's why Nofo is such a problem, he can score and cross the line, in fact I say he is a great try scorer. He just never works up a solid defensive pair with his center and score when he gets space near the line. Sheens will come up with the crazy play, that is guaranteed.
If Naden and Staines become the wing pair, it would not be the worst thing in the world. I can see both offering more in attack and defence then the Nofo/Mamaulo pairing.