Arteta should be blamed because he's the one managing the squad; whatever the problem is, he should be the one to solve and for him to be unable to solve the problem, he should be blamed. The same mistakes have been happening for seasons now, and you said the manager should not be blamed. However, if you are talking of players, Arteta is still the one to be blamed because any position that needed to be fixed, he would do that before the season got started to avoid the same issue.
He is a head coach and has responsibility for his club performance but surely there are other people in the club with their responsibilities as well. Arteta asked for a world class striker in latest seasons and he has never been given such a world class striker. In three latest seasons when they began more competitive and challenged Premier League trophy with Manchester City and Liverpool, their biggest weakness is at their striker position.
Is it fault of Arteta by did not have a very quality striker who should be able to score more goals for them than strikers they have now?
To win titles, Arsenal must be ready of spending more money for player transfer with a most urgent need of purchasing a top notch striker.