since the inception of Areteta he has spent almost £800 million or more than in the transfer market as Arsenal manager. So far no tangible result or outcome to back up this kind of spendings. I still can't understand how a team will spend so much money and still can't give joy to their fans. Arsenal is like a seasonal film where a new season is always expected every year.
So, true. If anyone is willing to watch a seasonal film or series in football, the better they watch Arsenal. 800 mio spent for three minor trophies, even one of these trophies are community shield. 
Seeing how Arteta is completely failed makes me believe he's not good enough to stay there. So far his target is only achieving UCL in any season.
That's why i totally aware how Arsenal's owner, Kroenke felt so reluctant in giving him money to rebuild the club.
Sure, I understand you may consider that as unsuccessful, but the reality is that they actually even like Arteta, because of the fact that they were even worse before him, so he at least made them believe that there is a chance they could win, and because of that they really like him, which I can see why they think like that.