I still think that comparing 9/11 to NOLA is like comparing apples and oranges. The WTC disaster was confined to a few blocks... The aerial view does not seem to agree with your assessment.
Moreover, you are counting only the horizontal damage and destruction; consider the sheer volume of the vertical damage and destruction (the WTC twin towers alone were 110 stories x 432,640 cubic fee per story x 2 towers) and you'll find the comparisons are valid.
Was the majority of Manhattan abandoned? Were the outer borough abandoned and under water.
I worked at the WTC. I know lower Manhattan well. IT IS A SMALL AREA. You can walk it all in 20-30 minutes. It was a tragic situation, but different from what we see in NOLA.