Yes, Arsenal have struggled to win the title for a long time because of mentality issues. I admit it, but Arsenal have improved quite well under Arteta. Arsenal need to improve their mentality if they want to win the Premier League title because so far they have been quite good in terms of performance, but this season has been too much for them to expect. Arteta needs to make many important changes in improving the team's mentality, but this is not a trivial problem to solve in a season.
The difference is, Arteta has not had one year to turn the mentality of Arsenal around, he has had 4+ years to do so. This is the 5th yearofArteta as Arsenal's manager yet the mentality has not changed. When you see the way Arsenal recruits players shows that they're not ready to compete among the top clubs in Europe.
Arsenal lacks a good attack. They could have signed attackers last summer but they didn't. Odergaad is the only creative midfielder in Arsenal and he's not a CM. Arteta focuses on buying defenders and defensive midfielders but they don't buy attacking players and its bad. With a team like that you will win games because Arteta is a good coach but when things get tough they won't be able to deliver. Arsenal is not going to win Real Madrid or win the League with an attack like that.
I don't know why Arteta doesn't see it but he doesn't buy attacking players they will win nothing.