Also its not only cutscenes but also quest design. Now you cant have for example a personal quest for Halsin that requires him to use wildshape to get past obstacles because the archdruid might not be a druid anymore.
This is an interesting point. I never realized it before, but it's true that the removal of class restrictions ironically limits design space. You can no longer have character-related quests designed around a specific class feature or ability, no matter how thematic or central it is to the character. I still remember how in BG2 when you were a wizard, you could eventually get your own demiplane and apprentices to train. Sadly that's probably not happening in BG3.
This also extends to items. If Lae'zel's personal quest leads to her finally wielding that silver sword she'd been dreaming about, it will be a very disappointing reward if she's a wizard.
