The problem is, Arsenal sacked Emery a few months into a season not long after he had Arsenal finish 5th on 70 points, after not being backed in the summer. Fast forward 2 and a half years, Arteta finished 8th twice, once after Emery being blamed for the bad first half of the season, then Arteta doing no better the season after. Then this season Arteta is about to finish 5th on less points than the Emery final full season, all while spending over £200m since being manager.
Not doing any better than Emery (actual done worse), while spending a lot of money in that time is actually pretty poor.