I am not an expert in ancient history, but if I am not wrong Greece was mostly composed of city states with different cultures, laws, family structures, sometimes temporary allied by militar leagues and temporary comercial agreements.... there never was a unified Greece or Greek culture until the greek population became the dominant ethnic in eastern Rome and became the new cultural elite at their own (even without Latins their identity was Christian Roman).

Even when fighting against Persians or being conquered under Alexander the Great where never truly unified, just common cultural traits.

The myth of a single unified Ancient Greek culture is a modern fabrication made during the rise of the nations in an effort of fabricate a common past for all folks living under modern states and give a legacy and an identity other than one of the provinces of Rome descendant of the ancient tribes who populated the peninsula. And my understanding is that the same happen with other European pre-romantic cultures like celts, Gauls, Britons, Germans and lots of other lost and forgotten mythological elements from Europe which were praised and recreated to differentiate modern states from their neighbors.