I'll circle back to previous objections to my hypothetical in a later post, and address here the "constructive theory" vs. "principle theory" issue. Einstein's history on this issue is also interesting and complex. Einstein always focused on creating principle-based theories. Obviously, SR is one such theory, with its two key postulates (constancy of c for all observers and constancy of physical laws in all inertial frames). SR led to some strange consequences, such as the asserted malleability of space and time, which must follow from the asserted constancy of c for all observers (b/c speed is measured in m/s or whatever units you prefer, reflecting space and time).
GR is similar, of course. But Einstein disagreed, however, with the notion that his theories were "just mathematical games" and he argued, to the contrary, that reality really was as strange as his theories asserted. He struggled with positivism vs. realism, beginning his career as a Machian positivist (only things that can be measured should be part of physical theories) and changed mid-career to a realist, arguing, for example, that reason alone required there be a relativistic ether, even though it seemed to be undetectable even in principle. This is the key example of where he began to break from Mach. Again, from his 1920 Leiden speech:
To deny ether is ultimately to assume that empty space has no physical qualities whatever. The fundamental facts of mechanics do not harmonize with this view... Besides observable objects, another thing, which is not perceptible, must be looked upon as real, to enable acceleration or rotation to be looked upon as something real ... The conception of the ether has again acquired an intelligible content, although this content differs widely from that of the ether of the mechanical wave theory of light ... According to the general theory of relativity, space is endowed with physical qualities; in this sense, there exists an ether. Space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any spacetime intervals in the physical sense. But this ether may not be thought of as endowed with the qualities of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.
And an interesting exchange related by Isaacson, in his biography of Einstein (p. 332):
“A new fashion has arisen in physics,” Einstein complained, which declares that certain things cannot be observed and therefore should not be ascribed reality.
“But the fashion you speak of,” Frank protested, “was invented by you in 1905!”
Replied Einstein: “A good joke should not be repeated too often.”