>There's no guarantee that the phenomenon we're interested in will be expressible in an F=ma manner. Complexity exists.

That's a fair point. But having a good theory doesn't necessarily mean that it's expressible as a succinct equation. The theory of how metabolism works is insanely complicated, but it's a good theory nonetheless, because every part of it plays a functional role, it explains a wide range of phenomena and it's logically compatible with other successful theories. None of that holds for deep learning models.