The Origin system prioritizes Larian content over the individual. Moreover, because they have an Origin system, the development and hours spent are invested heavily into a feature of the game that some may never use.
I played hundreds of hours in DOS2 over multiple campaigns and never completed an with any Origin character.
Already in BG3, I see that you are lacking content for things if you do not have them in your party. This was the same as DOS2. The Larian experience is predicated around having them in the party, you get a fuller game, more content, more cutscenes, more dialogue, more surprises.
But I should not have to take what Larian offers me in order to get the best experience. And Swen/Larian can say all they want that they are making it to where custom parties have the same level of quality, but I know that is not true.