As you say, an informative article. In addition to inadequate levees, the subsidence of the city also contributed; up to 3 feet additional protection needed, but somehow the subsidence not being measured.
It is questionable whether the levees, even if they had been strengthened and raised, would have held if the full force 5 hurricane had been directed to the city, rather than to the east and the Gulfport area.

The removal of fluids (oil, gas, water) from the subsurface anywhere around New Orleans must stop. The more the city sinks, the higher the levees must be. The subsidence perhaps could be halted by pumping in water, but this would also be an extensive, expensive process. The emphasis now is on oil recovery, not restoration of the subsurface, so more subsidence will occur.

And- 1900 sq. miles of coastal wetland has disappeared over the last 50 years.

See article from National Geographic Magazine, October, 1904, covering subsidence and loss of lands, and making a prediction. One year after, much of the prediction comes true. The car-less, the poor, left to the mercy of the rising water.
Louisiana Bayou