Arsenal had consistency performance in last two season but keep can't reach the higher round in Champion League after this season eliminating from quarter final round.
Arsenal performed well in domestic league keep pressure Manchester City until the last matchday before winning Premier League trophies in Champion League they can't performed well as consistency in domestic league.
Arsenal seems lack winning mentality on many crucial matches when facing top teams, I doubt next season their perform well in Champion League if the knock out round or quarter final round have to face top teams such as Bayern Munich or possibility have to face Real Madrid. Arteta need improving his teams with winning mentality against the top teams and Arsenal is the only of big four Premier League teams never winning Champion League trophy.
I'm still curious about what happened to Arsenal, they were always able to maintain their performance at the start of the season, but as the season approached the end, their performance slowly started to decline. This situation really affects their progress in the Champions League, failure is often experienced due to not being able to compete with other teams. The Champions League is more competitive than any other league, you need to maintain your performance to reach the final round.
Arsenal must bring in quality and experienced players in winning trophies, their presence can help Arsenal build a winning mentality. Arteta, who has succeeded in improving Arsenal performance, must focus more on his team's performance, which often slips towards the end of the season. A strong team mentality will enable Arsenal to compete with other strong teams.
Arsenal's weakness is that they cannot maintain consistency until the end of the season. As you said, Arsenal in the last two seasons at the start of the season played very impressively but entering the second half of the season they seemed to have lost stamina. This will probably be a serious job for Arteta so that next season he doesn't repeat the same mistakes. because Arsenal's game under Arteta was actually good, it's just that Arteta didn't dare to rotate players, which made his players tired.
Arsenal this season failed in the EPL league and also failed in the UCL league, this is because Arteta played too many core players without rotating players so that in important matches they could not perform optimally. It must be admitted that Arsenal and Bayern Munich's performance this season was actually better than Arsenal's compared to Bayern Munich, but because Arteta couldn't take advantage of it, they ultimately lost to Bayern Munich in the quarter-finals. So in my opinion, next season Arteta will not only buy quality players but he must also have the courage to rotate players because this is to maintain the players' fitness and stamina.