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.
Arsenal will need to bring in some new players to improve their squad depth in order to compete comfortably in these two tournaments. They require it even more today, given how their season ended with them losing the Premier League title to Manchester City.
One of the major reasons was that some of their core top 11 players were injured, and there was no better alternative to fill those spots, therefore they performed poorly and gradually lost the title fight to Manchester City. They need a more powerful and agile team now; they must be fit and compete well in both their domestic league and the European competition.
I wonder why they didn't take care of it in the winter transfer window, because wasn't it clear then that if someone got injured it would be difficult to continue? Apparently they realised this and either didn't find anyone worthy or didn't dare, the result is evident...