The impossible thing for Arteta to do is to waste time in the champions league, because they have always entered the champions league so far so it is very difficult to say that the champions league is just a formality match for Arsenal, while there are many teams out there who want to enter the champions league.
The champions league is indeed very extraordinary and yes Arsenal need to pay attention to their team again to be able to compete, some substitutes as a second choice when one of the core players is injured they have a substitute who is worthy of competing and can carry out the same task and in ability and performance should not have a very far difference between substitutes and core players because it will be very heavy in a team.
Arsenal need to plan to do well in the Champions League in the same way that Real Madrid plan to win the Champions League trophy. They should consider the Champions League tournament as mandatory, leaving the Premier League as a secondary option, but they will do well in the Champions League
Arsenal are good but we also have to realize that in the end we can see Arsenal's performance is not that good when talking about competition in the Champions League. Not only in the current Arteta Era but indeed from previous eras even during the golden era they were unable to become champions because their best phase in the Champions League was only up to the final and that happened almost 2 decades ago.
Indeed, I know that in the end Arsenal are still very good for a club but in the Chmapions League they have to be better than now if they want to be juxtaposed with some big clubs who are regular champions in the Champions League because for now Arsenal still don't have that kind of capacity.