The city of New Orleans, citizens, politicians, and U.S.Corps of Engineers were delelict in their duty to protect the city with substantial dikes/leveesto keep out the water. One trip to the Netherlands should convince any one with common sense.
Pumping stations with self powered diesel driven pumps on standby would be a second requirement.
The question is spend money to clean up the mess, provide adequate protection for the potential flood area, and rebuild, OR start over from scratch and rebuilt elsewhere?
I’m not going to address the rest of your post, because that sort of thing has already ended up in The Pit. But, would you mind defining what a substantial dyke/levee is? Sure, you could prepare for the once in a million years storm, but at what cost? Also, if I’ve heard everything correctly - the levees are in place to prevent flooding by the Mississippi. And the levees prevent the deposit of silt in the coastal wetlands, resulting in their shrinking. Those wetlands have served as a break for storm surge in the past, but with less wetlands there is less protection.