#1 Keeping a weak bench
Mesut Ozil, Jack Wilshere, Aaron Ramsey, Laurent Koscielny, and Hector Bellerin were rested for this game, with Wenger's focus clearly on the Europa League for the remainder of the season. While it was a right move from the outset, it backfired in the context of this match alone.
Arsenal had no one to turn to on the bench after United took the lead in the 68th minute of the game.Youngsters like Joe Willock, Ainsley Maitland-Niles, and Eddie Nketiah were given opportunities, but could not grab their respective chances on the day.
The Gunners lacked creativity in the final few minutes of the game and the attacking impetus seemed missing from their build-up. Overall, it was a forgettable display from the North London side.