In general, I think the distribution of cultures is good. There are nitpicky placement issues (like my stupid Tocharian, Khwarezmian bullshit a few pages back) but the cultures you've chosen to represent are largely solid and major participants in the history of the time. The existence of smaller cultures, for example Galatian which I saw mentioned a little while ago, doesn't mean they should be included, not to undermine their role in history, but because they represented no majority, did not hold independent political power and had mostly been displaced. This is why I don't think it's meaningful to include cultures like Corsican, Sardinian, Sicilian. What do they represent and are they sufficiently different from their neighbors and each other to warrant representation? Are the differences between Geats, Norse and Jute political or cultural? Lastly, I don't think cultures like Suebic, Vandalic and Hepthalite held majorities in the areas they conquered. They were ruling classes over an ethnically and culturally different population. They should definitely rule over these places, but I don't think the places themselves should share their culture initially.
For the purpose of balance, it hurts the game to create significant cultural fault lines where they probably didn't exist.
I see, but the reason some smaller cultures exist is because some of them are important. The Isuarians and the Laconians were participants in history, and were a majority in their own areas. And the Corsican, Maltanesse, Sardinian, Silician, Galatian, and Pontic cultures give neat possibilities. They are small, and will soon probably be wiped out, but to see a Galation warlord create a Celtic Anatolia, or the Corsican language becoming the language of the Kingdom of Corsica (Italy). Those little possibilities give minorities a chance, a chance that a Pontic rebel will liberate a new Pontus. Normally, you will see wide cultures, but the minorities make the game more interesting. In a play-through, I got a Massalian in my court as the Visigoths. He became my steward, and little actually happened. But it was neat to see a minority appear in game.