The "true market" is like "no true Scotsman" or "a closed system" or "a spherical cow on a frictionless plane". It assumes something that doesn't exist. In economics the influence of the things it assumes wrongly can be very significant. In physics wrong assumptions can also make the results wrong and a lot of work (or rather most work) is done on checking if all the assumptions are sound and ensuring that the influence of the remaining gaps are negligible. That is something that is hard to do in economics when it involves interactions with the global market.
Yes, special theories can be precursors for more general theories.