I think the origin character thing largely comes from how they handle multiplayer co op. So they have characters starting at the beginning in the same basic situation. Those characters are all able to take the lead in dialogue and other situations.
It would be nice if there are other companions you can meet later who are more like followers, but with actual personalities. That should allow for more proper party members without needing to allow them to do everything a main character can. Maybe.
Although I wonder if some origin characters really need to be rigidly tied to a class. Astarion’s main deal seems to be being a vampire spawn. How central to his story is being a rouge? Maybe a lot, maybe not much at all? It might be worth allowing players to respec orgin characters, with the warning that some dialogue will be a bit out of place. It could be a strongly not recommended option, but still an option if someone is set on particular party composition, but doesn’t want a bunch of nobodies.