#2 His previous success

His success in the Europa League is undoubtedly exceptional, having managed to win it on three consecutive occasions with La Liga side Sevilla. That, coupled with his big-game experience, will prove valuable for Arsenal's progression in the competition this term - who knows, they might actually win it this season.
He won seven trophies during his two-year tenure with PSG and has also won the most trophies since 2015 - 10 in total, which is more than both Zinedine Zidane and Pep Guardiola, who are regarded as two of the world's best managers.
Although he might not be the big name that many supporters and critics alike were expecting, his appointment is a shrewd one and could prove successful in the long-run, so respect and recognition of his achievements must be granted.