I like Tierney, but I feel that he doesn't have the technical ability to do what the manager wants, so it is best that he leaves. It's a valid question to ask whether Arteta's wishes for this team are the best way to go, but as matters stand Tierney did not suit our way of playing and I am happy for him that he has gone to a CL team.
More generally, I think that the loss of Timber has been a hammer blow to our prospects. Aretta is clearly trying to work around this, but my concern is that rather than altering his approach to get the best out of certain players, he is stubbornly sticking to a plan that only really worked with a player now out for the season.