By definition an LLM is unable to build what has never been built before because you are going outside the realm of pretraining/RL. You might be able to combine components that already exist in a unique way, but even then you will be fighting against the mediocre making effect of LLMs
That understates what LLMs are capable of doing. They can and do build things outside of their training dataset. As long as you can get there by following existing concepts, they can do it.
That’s a hard position to defend in the face of navier stokes
That seems nonsensical. Consider a selection of even just 8 types of components or patterns that might be in a training set (or available to be found over Google and fed into a prompt by a harness, for that matter). There are 256 distinct ways to use 1-8 of them together.
And of course the number of libraries, known algorithms, etc, is much larger than 8. There's any number of ways to make something new by combining well-understood parts.
I don't think non-expert prompting is pushing the envelope on what can be built because I think the current generation of harnesses and models pushes to using well-understood patterns in well-understood ways but it's certainly moving the line for what has been built. And with more skilled prompting you can build pretty crazy stuff + extensive validation for it.