I thought the whole point of trying to write out TLA+ is so that you get a better idea of what you want and put it into formal language?

I get that an LLM can assist/help with expressing what we want in formal language a bit, but if one automates all this there is no human intent/design anymore.

If the LLM generates both the design (TLA+) and writes an arbitrary program that satisfies said design -- what exactly have we proved?

What assurance do humans get since human doesn't know or cannot specify what they want.