I very much disagree. Maybe Pommerania shouldn't be formable, but it should be clear its a separate region from germany, denmark or poland. Maybe that's the best solution to "fantasy" kingdoms (real fantasy, not africa fantasy which actually existed).
On topic to byzantium. Since the whole name byzantine empire is stupid and its system fictional (or well the same as western-europe, which is... not accurate), I think it is safe to say that we can safely split it up in 4 kingdoms for better balance (and make it easier for the empire to collapse, I still have yet to see that happen).