Yet you ignore:
Xhaka was one of our best players against Newcastle. This isn't a criticism of him. This is an example of how Arteta could have changed things to disrupt a very structured unit with a right footed dribbler who loves to cut in, rather than a left footer who naturally goes wide.
There is a difference between a player 'not being good enough' and acknowledging that a system could be changed to suit the game state. Your confirmation bias ignores the fact that Xhaka has been one of our best and most effective players this season.