The problem in San Francisco is entirely different. It's on poorly designed building. Even if every building in San Francisco had that problem, it still wouldn't be relevant.

The problem strata in New Orleans is the top 10-20' of soil. Mostly whatever's above the pumped-down, controlled, water table.

Piles only need to go that deep to suffice, or more typically until they hit the first layer of sand, which is stable. Literally every slab house built in New Orleans is built in these, because before this, everything was on blocks so it could constantly be raised and leveled.

Does having poor soil mean New Orleans buildings are designed better? Or does New Orleans suffer from both bad soil and designs?

It just means everything gets built on piles, so there's a lot of local experience.

I wouldn't say better, because there are/were multiple skyscrapers with chunks of facade falling off them. At least a couple are abandoned because they were built so bad.

But they're not sinking.

>or more typically until they hit the first layer of sand, which is stable.

I think this is the first time I have ever seen someone claim that a layer of sand is stable. But hey, NOLA is one of the craziest places, so sure, sand is stable there.

We're not talking about a beach here.

Sand underground with overburden pressure is quite stable, to the point that piles driven to it are treated as bearing piles (supported primarily on the end/tip), not friction piles (supported on sides by friction).

It's non-cohesive, so doesn't shrink or swell, and once it's compacted/consolidated, it's fixed volume and quite stable.

Yes, AFAIK the piles didn't go all the way down to solid bedrock and San Francisco is basically built on a garbage dump covered over from previous devastating earth quakes, basically. They were improperly installed and if they had been the building would likely be fine. So, you're both right.

That area of the city is built on infill, but that is by no means true of most of the city’s area.