He doesn't need to work on the defense, Arteta already has the best defense in the Premier League, he also have the best defensive and central midfielders, that was what he used years to build in the club, what's remaining to work on is the attack which will be the focus for this new season. If Arteta works on his attacks, score more goals and defend them, winning the league will be at his court.
I absolutely agree! Arteta has the best defense not only in the PL but also CL actually. As far as I know they finished the CL as the least conceding team this season.

He only needs to work on productivity with goals, yes. Gyökeres should be more in action. But for that they need a winger who will feed him instead of being more selfish. Saka isn't such profile so they had better sign one for left wing...