I don't know why Arsenal don't more often employ the strategy of buying up good players from smaller clubs in the league. Juve do it, Bayern do it, Utd used to do it a lot. I was surprised at Dunk's stats, he's doing very well this season. Evans, Maguire & Lascelles are all CBs I'd be happy to consider too. But none of them get above 80% for pass completion and I'd bet that's the sort of thing that puts Arsenal off, even though you complete more passes in a better team. Whoever it is, Arsenal needs a CB with game intelligence and organisational abilities to partner Mustafi. Mustafi is a doer and he's good at that, but he needs someone next to him telling him what to do.