> language

dialects with regional substrate and vulgar varieties; koine written greek is a rather late standard, perhaps not byzantine, but koine literally means "written", in contrast to spoken.

> lifestyle

like what? Sedentary, sure.

> music

music-ians, who were not the same everywhere

> alphabet

again, regional variants exist, writing style wasn't fixed

> commerce

commerce is competition, so how could it be unified? associated towards outsiders, perhaps.

> military style

I wouldn't know about that, but Sparta vs Athens thousand years earlier would be a common counterexample

It's debatable how hellenized the Greeks on the anatolian cost were, the Lydiand, moesians and cetera. "barbaros" relates to speech first and foremost, though I am not buying the etymology. Speakers of other mother languages would have reasonable trouble getting the pronounciation right, so a Scythian, Tracian, Dalmation or otherwise "Celtic" Slave would appear hard to comprehend.

If you are generalizing a millenium of history, you are all history barbarians.

Your argument is "there were dialects and local variants". That was true everywhere until 1st WW and mass media.

Could we agree that Athens and Syracuse were more similar than Athens and Persepolis?

How about common myths and goods? Olympic games that paused wars? Delphi were in "center" of helenic world? And ancient debate if Macedonians are "true Greeks" or "barbarians"?

Innovations and technology were at the same level and culture was propagated and expanded easily among the different cities but they were by no means unified, look at the social and political structure of Athenas and compare it to the ones at Sparta, almost two different worlds, military technology, strategies and formation were different, heirs and inheritance had very different rules, arts were very different, even the view of life and understanding of the world was very different... they might have look similar as Phoenicians or other bronce age, early Iron Age tribes from the region, specially since through commerce and piracy there was a permanent exchange of products and ideas.