I agree with you. In the past few seasons, we have seen Arsenal buy players at high prices, but we do not see the expected performance from the players. Arsenal must be careful about buying players and at the same time be smart. Otherwise, even after spending a lot of money, the squad will not improve.
Coach Arteta is experienced. Arteta must find the weaknesses of his squad. At the same time, he must find players who are suitable for Arteta's match strategy. Otherwise, even after spending a lot of money, Arsenal's performance will not improve. But personally, I think Arsenal should strengthen their bench team more now if they want to continue their good performance.
I totally agree with you about how Arsenal buys players. Team has spent a lot of money on new players in last few years but they have not always played as well as expected. To really make team stronger Arsenal needs to be smarter about who they buy. They should choose players who fit with coach plan. Also as you said they need to make their backup players stronger. This will help them keep playing well even when their best players get hurt or are too tired. If Arsenal can do this they will be able to reach their full potential and have long term success.