1) We're actually not really arguing against one another. I did not mean to say that they had less complex political structures; I don't think that was true (at least not across the board).They hardly had a "primitive" political structure (you would have to define such a structure in the first place), and lack of writing is something that people have to stop using as a sign of "primitiveness". The Celts had writings anyway, with various pre-Roman conquest Celtic inscriptions having been found. It can be argued that the Roman conquest just happened to eradicate all major Celtic written works (similar to what happened with the Achaemenids after Alexander devastated Persepolis and Susa). After all, the great majority of Greek writings perished as well and only a minority survived.
2) I suggested a scarcity of written sources from them as a reason for their being relatively "dark" in terms of historiography. A culture always appears more sophisticated to us when they're writing a lot, especially highly abstract stuff like philosophy.
3) I know Celts wrote, but they were not an intensely scriptural culture. Instead, we must assume many of their more sophisticated cultural concepts were linked to orality.
4) the majority of Celts from Hibernia to Galatia were not subjugated in destructive wars by the Romans (and some indeed not at all), so that's only a limited argument.
I doubt that. Druids were powerful Men as it was, and they were likely responsible for much of what made up Gallic identity and ideology, to use an anachronistic term. If a more centralised state should arise in Gaul, I"m sure it could only be brought about by a military "strong man" (there was a number of them around), so a Gallic Empire would likely have a powerful worldly ruler who'd try to use druids to his ends, and to the extent to which they wouldn't conform, he'd see them as a political threat and attempt to sideline them.I mean the celts seemed to have a fair level of organization, especially with reguards to their religion.
If they were to form a state*, I would put my money on it nucleating around their druids
*keep in mind that using the concept of "states" is really anachronistic here, as its more or less a modern invention and wasn't really a solid concept until the french revolution