Two separates book would be the same. The problem was that it was a initial book like SCE, not a mixed book. We have Aeldari as an example of a mixed book that was flavour, complete and with múltiple styles of play.
They never balanced with BW in mind, they started doing that after It reached the 60% of winrate and points were not touched outside Prophet, they continue decresing all Ironjawz and Kruleboyz points every Battlescroll.