It took just as long as it did during hurricane Agnes. People were on their roofs then, too. People didn't start looting or killing each other, either. They were as grateful as hell when the troops showed up. They said "Thank you", not "F you."
Those people were suppose to evacuate. They didn't. Now, people are trying to help them as much as they can. There is no magic wand.
You're totally ignoring the brave people who are down there in great numbers wallowing in the sewer water to save those who decided to stay with their "stuff." Give the good people helping down there a little credit for a change. They're human, too, and they're being hassled and shot at. They're doing the best they can.
And I think that has always been the side of humanity we've seen in disasters past. I know I wasn't prepared to see such evil run amok in this country, and even the innocent will be viewed with suspicion as a result.
Hey! Your don't need to tell me about Hurricane Agnes. I went through it in a very rural mountainous region and we took care of ourselves. These people have no way to take care of themselves. They are stuck in city where the mayor is completely incompetent.