#1 Arsenal don't have quality midfielders for a 3-5-2 system

Even though Emery retained the same XI that hammered Valencia 4-2 in the semi-final second, the superior opposition they faced in the final clearly brought out the chinks in their armour. In all successful 3-5-2 systems like Antonio Conte's famous title-winning Chelsea of 2016-17, the midfield is run by two energetic box-to-box midfielders, with superb passing range (N'golo Kante and Nemanja Matic for Chelsea in 2016-17), supported by a hard-working playmaker, who comes back to defend when the wing-backs are caught up in forward positions (like Cesc Fabregas for the 2016-17 Chelsea outfit).
For Arsenal, they simply dont have the personnel in midfield to run a 3-5-2 system successfully against a quality opposition. Ozil is not known for his work rate and last night, it came to the fore as Chelsea overran Arsenal in midfield, with wing-backs Kolasinac and Maitland-Niles often stranded in forward positions. Mkhitaryan would probably have done a better job than Ozil. This, combined with the limited passing range of Granit Xhaka and Lucas Torrerira meant that Emery couldnt leverage the normal advantages of a sound 3-5-2 formation. In direct contrast, Chelsea's metronomic passmasters Mateo Kovacic and Jorginho controlled the rhythm of the game right from the onset and refused to let go of their chokehold on the midfield till the final whistle