Not A Poet
Not being an insider, I certainly can't cite specific details. But, as LR indicated, a machine the size of NYC does not operate in a vacuum in the face of such an emergency. It requires leadership and the mayor is at the top of the "food chain."
More appropriately, if you don't believe he contributed significantly to the recovery effort then it behooves you to say why and where he failed. Remember, innocent until proven guilty and all that. Since he was in charge and things went extremely well, he deserves credit until some evidence uncovers that he failed and someone else actually directed the efforts.