Aside from the mega dynasties and merging of dynasties across the board, we also have a handful of broken dynasties (Chola in the Tamil Kingdom), one man was made an infant on shaky historical grounds and he still retains his daughter who is, in fact, older than him in 1066 (see charID: 33369 in Saxon character file). We also had got rid of some placeholders, it's nice to see, but some were just replaced with others.
I'm not too sure why we need mega dynasties at the game start. The vast majority of them do not have credible historical connections and are simply remnants of CK1 and CK2 which were plagued by naive developers listening too much to WordPress genealogies and hobby historians than more credible sources, and that was fine then because dynasties didn't really matter much. Examples include the renamed Luipolding dynasty with many cadets like the von Babenberg, the Etichonen dynasty houses both a notable french house and several historical houses like the Habsburg despite this not being provable, the Karlings are also an even bigger mega dynasty now with the Wigeriche in 1066 and a few others etc. The Salians are now part of a big chain of Lombard houses, with the most incredible connection being an educated guess based on onomastics with the founder's sons. Most if not all Breton dynasties are related in some fashion not even supported by legends, which means Count Cerneu in Cornwall and the Duke Rennes in Brittany are actually related and will inherit each other despite the most recent common ancestor is from the 4th/5th century, completely bogus. And more and more, let's not talk about the Irish.
I hope they can do something about this. It might not be such a big deal in the grand scheme of things, but if not for history's sake consider the balance of renown and easy inheritances.