Mustafi, quite understandably, looks far better playing alongside the outstanding Koscielny. He is also still in his first season with us and his first season as a big money signing. I am not concerned.
Xhaka has been unlucky. His first red was a joke and his second somewhat borderline. I hope to see more of him. If we have a weakness I am sure it is in midfield (wide forwards could be a bit better and a top class left back would be nice, but you know what I mean)