Even though they've been better in recent weeks, the worst thing about Xhaka and Mustafi is that they're a bit thick. They have no street smarts on the pitch. Mustafi especially always seems to go for the wrong option in any pressure situation.
Considering we've moved on from Wenger and we're still being punished by cheating players and refs each week, the biggest improvement Emery could make to the team is implementing the tactical fouling United, Chelsea, Spufs and now Citeh have always gotten away with. That, and buying some scumbags like Ramos, Alli, Big Man and Busquets that are immune to the rules. Oh, and also make sure Lacazette and others throw themselves violently to the ground when they feel any contact rather than trying to play on.
Being a cunt is obviously rewarded greatly in this sport so it's time to embrace it.