#2 Not replaced Santi Cazorla

In the past 3 seasons, Santi Cazorla has missed 79 games through injury for Arsenal. The Gunners have sorely missed the Spaniard as he offers a style of play none of the other midfielders can replicate.
Cazorla is a creative CM that can wriggle out of tight spaces, create chances from the middle third, link midfield and attack and score set pieces.
His close control and agility allow him to relieve Arsenal of opposing teams that press in cohesion. His trickery thus creates space for others as defenders are drawn to him. Such a creative presence helps take Wengerball to new heights where they can actually compete for the title.
Without that creative presence, Arsenal are a redundant uninspiring team. Arsène Wenger has once again gambled on the fitness of the 32-year old instead of replacing him, and now the Gunners will not come close to the title again.