Well, I definitely agree that the game is somewhat lacking depth and variety in a lot of aspects. Former things that CK2 had and that a new game should bring the possibility to improve have been completely scrapped only to be sold post launch.
College of cardinals (sure, CK2's implementation wasn't the best, but it was one of the first DLCs launched, 2013!) is totally missing, and we don't even have a mechanic to allow for faiths sharing a same Head, which is disappointing.
Byzantium lacking any form of special treatment aside of Primo unlocked, which is ridiculous. In CK2 devs always said that code was too feudal-ey to do the byzs proper justice and that that was why they would always be lacking and difficult to manage. Yet a new game comes, the perfect opportunity to get things right, and they're an outright feudal government with early primo. And code still seems extremely feudal-ey seeing clan government is essentially feudal but relying on opinion instead of contract.
The hundreds of events related to cultures, religions and governments that are missing. I've had a full Zoroastrian run from 867 to 1453 and there wasn't a single event related to Zoroastrism, aside of the generic ones related to lifestyles that just change God by Allah or Ahura Mazda or whatever. That for me is just extremely disappointing, because the differences between playthroughs get so narrow that it becomes repetitive really fast.
So yeah, religion system and visual aspect of the game has been remarkably improved, can't deny that, but in a lot of other things the game just feels the same or even a downgrade from what we had in CK2.