He frequently experimented with different formations and strategies, which led to a lack of consistency and an inability to build a cohesive team identity. This was reflected in Arsenal's performances, which were often lacklustre and uninspiring.

In addition to tactical and identity issues, Emery also had problems with man-management. He frequently made puzzling decisions regarding team selection, which left fans and players alike scratching their heads. 

He also had a difficult relationship with some of Arsenal's star players, such as Mesut Ozil and Granit Xhaka, which led to tensions within the squad. This was reflected in the team's performances, which often lacked the energy and enthusiasm that is necessary to succeed at the highest level.

Finally, Emery's struggles at Arsenal can also be attributed to the high level of competition in the Premier League. During his time in charge, the league was dominated by teams such as Manchester City and Liverpool, who had significantly more financial resources and talented players than Arsenal. 

While Emery was able to guide Arsenal to the Europa League final in his first season, the team struggled to compete with the top teams in the Premier League on a consistent basis.

In conclusion, Unai Emery's tenure as Arsenal manager was marked by inconsistent performances, a lack of identity, poor man-management, and fierce competition in the Premier League. 

While he was able to guide Arsenal to some impressive results, such as the Europa League final, his tactical approach and man-management style ultimately proved to be his downfall. With Mikel Arteta now at the helm, Arsenal are looking to rebuild and return to the top of English football.