Cazorla and Coquelin were the best CM pairing we have had in years.
His form has dipped and he isnt playing to the level he once did, and i agree should be replaced. However not long ago he was performing to a level unrivalled by any DM in the league.
If Ramsey has taught us anything, its that footballers levels arent consistent or always on an upward curve until the curse of the 30+.
However, given that you think Arteta was a good DM, id keep your opinions to yourself.