The whole myth is inconsistent. The Czech version doesn't even mention Rus' at all, and both Czech and Polish versions are focused entirely on their respective origins with the other brother(s) being side-characters.
I, too, don't like that the South Slavs get left out but it kinda does make sense because they're separated from the West and East Slavs by the Magyars and Vlach (who are not Slavic, Paradox - Romanians are not Slavs)










