I agree with you and I also see that the weakness lies in the mentality. Almost all of Arsenal's players have great abilities, but they lack the mentality that has led to their failure to win the Premier League title in the previous three seasons.
Arteta needs to improve the players' mentality when facing competition, as they have so far lacked confidence.
Finishing second in the standings for three seasons isn't bad considering the quality of the players Arsenal have, so they need to develop a winning mentality for next season.
I disagree with you that Arsenal's failure to win the Premier League title was because they lack a winning mentality because if Arsenal players lacked a winning mentality, there's no way they could win a lot of matches in the Premier League, which is tough and competitive, and finish in the second position in the Premier League table in 3 consecutive seasons. Arsenal players are hungry to win their matches, and they have a winning mentality, and we have seen it in them since Mikel Arteta became Arsenal head coach. I think Arsenal's problem for not winning the Premier League title is injury and lack of a quality striker, but since Arsenal has agreed on a transfer fee for Gyokeres this season, if Arsenal's key players are not injured by the end of next season, Arsenal has a great chance to win the Premier League title.