You're not wrong about any of this.
I used to work for EL as a process engineer in manufacturing where CDLM is made. Therr's a lot of lore and history around it.
Max Huber was a NASA scientist who suffered from chemical burns in am accident. He dreamed up the La Mer essence and would put it I to Nivea body cream as a treatment for his burns and invented La Mer.
EL bought it and makes the essence in-house in a process that they keep under fairly tight wraps but really, I think it is just quite specialized and they don't make a lot of it, so it happens in some dark corner so it doesn't interfere with the rest of production. I know it involves putting the marine extract into a tank and passing sound waves through it at a specific resonant frequency and it takes about a month.
La Mer essence was always provided as an ingredient, ready to add. But they do, or at least they used to, sell pure essence and there's nothing stopping you from getting it and mixing it in to Nivea body cream or any cream of your choosing. Or use it straight.
The cream itself is really annoying to make and has really strangely specific directions that make it weird. Most cream are oil droplets dispersed in water to make an oil in water emulsion. CDLM starts like this but "inverts" during mixing to become a water in oil emulsion.
The batch has to be taken out of yhe mixer during cooling at a very precise temperature window. Miss is by a degree and the whole batch is rejected. Sometimes it doesn't invert properly and gets rejected.
This is such a dicey process because Nivea body cream, which is what this is based upon, is made using a continuous process (where every ingredient is fed into the pipe as it flows) but it is now being made as a batch process.
The high rejection rate (and there are several other points where rejection is high) is part of the reason for the high cost. All of the issues contribute to the cream sitting in a lump in the middle of the jar and pulling away from the sidewalls and eventually some of the water weeps out into the space next to the wall. No one is sure why, thus the high rejection rate trying to stop the problem.
The magic of La Mer, if there is any, comes from the marine essence. Nivea body cream was nice and thick and greasy which made it great for wound healing and that's why it is a heavy cream.
Now there are other versions of the cream and other products in the line, but the marine essence is the only important ingredient.