If you have a purely instrumentalist view of reality, where, as I said, your so-called knowledge is actually just a model of an unknown thing which you employ to predict the measurements you read out against a ruler or on a meter or something, then yes, we've made progress exactly of the kind you describe.
But I was trying to make a point about epistemology and ontology. Physics has actually been pretty catastrophic for ontology. I don't think its wrong to say that from the point of view of physics we simply do not know what anything actually is.
> I would also argue that the only things we can "know" are what you call the instrumental definitions. We only know what we measure. The rest is interpretation, and self-consistent understanding.
Yes. But this is a fairly radical position historically and philosophically. Most people would say that there is more to existence than measurement and I while I share your instrumentalist sympathies, like most physicists, I don't see the philosophical case that we can have a consistent worldview if we denounce all knowledge not related to measurement as a total non-starter.
Think about what instrumentalism really means. When you utter the sentence the earth is an oblate spheroid, you are actually making an incredibly complicated set of statements about the outcomes of experiments. If we take the instrumentalist view the measurement doesn't actually tell us the earth is an oblate spheroid - it just tells us that if we make a series of measurements then they come out in such a way as to be concordant with a model of the earth as an oblate spheroid. Are you really prepared to give up the idea that the earth is a thing you can know about?
I actually rather think physics strongly encourages us to adopt the instrumentalist view, primarily because it seems so clear that physics has a local character. In GR there simply is no state of affairs whatever about what is happening "right now" except at the point in spacetime where you make a measurement. Really think about what that means. If we are standing at the north pole and make a measurement of some kind, how can it pertain to the earth as a distributed object in space when we know GR says there is no state of affairs pertaining to that object at the moment of the measurement?
GR tells us all about what the outcome of various measurements will be, but it also calls into question what precisely those measurements might mean. The instrumentalist is committed to the idea that the only thing we can talk about is the results of measurements. What the measurements operate on is just not something we can know. I think that's weird. Physicists often conflate their mathematical models with reality and that lets them think an instrumentalist view is sufficient: the measurements coming out such and such a way is taken as evidence that the universe is filled with objects consistent with the model. But that association is non-trivial in modern physics.