Western European Celts had a rather technologically advanced culture and, in some regards MORE technologically advanced culture than the Roman (remember steelmaking)... still they didn't have stable states. But if we take Archaic Greece they didn't have such states either. I think Celts needed two or three more centuries to build more or less successful feudal society... and don't forget Roman divide-et-impera policy in Gaul in II-I century BC. Maybe without these efforts Arverni or Aedui could succeed earlier.

We have an example when tribal society ALMOST succeeded in building advanced state - Dacians. If they didn't have Trajan's Empire against them...