1) The theatrics. 3D cutscenes absolutely don't limit what you can do with your voice actors after me ( As far as I understand that's what you implied here) BUT it does impact the end result. I think that's one of the main reasons Shadowheart for instance seems to be aggressive for no reason while without the close up on her face her words could sound differently. And that's why some jokes are delivered in one way rather than another.
2) Adapting the narrative to your technical limitations is a thing but when it comes to dialogues it's better to have the voice convey what you wanted to convey and worst case scenario the body language won't always follow together with it(The face most importantly will "suffer").
Based on what BG3 is+ the interview with Sven + common sense -> No, they intended to tune down the goofyness. But nevertheless, it's an interesting subject.
Right the voice actors will do what they do, but if the 3D is not their to match the act, everything sort of falls flat. Just like in stand-up comedy, body language and timing is almost as important as the joke itself, and some jokes rely entirely on that.
Overall most scenes and dialogue feel subdued and I think it's because of the 3D. The narrative and the writing suffers because they understand what they can and can't do with their cinematic approach to everything. I'm only speculating that this is intentional despite what Swen is saying. It's convenient to say you're make a more serious game without the gags because under the hood they have some creative limitations that they are fully aware of.