A stronger team is necessary given the competition in the Champions League and Premier League. Arsenal must concentrate on having a strong bench team in addition to strengthening their starting group. Key player injuries are a real possibility and without a reliable backup the team performance as a whole could suffer significantly. Therefore in order to properly handle the demands of both tournaments Arteta and the club management must place a high priority on squad depth.
I would say Arsenal is a strong team as it is and is still capable of fighting for the title of the EPL. I agree with you on the need to concentrate on having an equally strong squad as substitutes for the starting eleven. Arsenal witnessed some setback when they had some key players injured and no one suitable enough to fill in the roles of the injured player. Without suitable replacements to fill in these roles when needed, the performance of the team would suffer setback as witnessed by Arsenal.
They would definitely need to make some drastic improvements as they’ve now qualified to be in the race for the title of the UCL. They would meet and play against other top clubs from other leagues.