> * That can still yield useful "discoveries" in certain fields, absent the discovery of new mechanics that exist outside said training data

One can argue, new knowledge is just restructured data.

I think the main concerns about LLMs is the inherent "generative" aspects leading to hallucinations as a biproduct, because that's what produces the noi. Joint Embedding approaches are rather an interesting alternative that try to overcome this, but that's still in research phase.