Once people talked about "iron horses". Now we have walking robots. From a current perspective, trains are nothing like horses; does that mean that it's invalid to say designing and making walking robots does require/provide insight into the physiology of legs?

It seems to me you're making a very general statement that there is no progress in understanding because people used to vastly overestimate their understanding. People did not know stuff, and therefore they will never know stuff, and therefore they do not know stuff.

I'm not arguing that our understanding hasn't advanced, only that our models are constrained by our internal conceptual and external verbal/written vocabulary. It's possible that brains are doing things that we have no thoughts or words for because they don't resemble any system we've ever dealt with.

> does that mean that it's invalid to say designing and making walking robots does require/provide insight into the physiology of legs?

Yes. That sounds invalid.

That sounds overly binary to me. (said with conscious irony)

You are saying that the informational inputs and outputs for walking robots have exactly the same amount of relevance to biological limbs and biological control of walking as the engineering of steam locomotives?

Obviously they have aspects that are nothing like walking creatures. But the more they solve the same problems, the more they have to be similar, either intentionally or accidentally.