The concept of origin characters is a little weird. These are the NPC companions, why would they also be playable as the PC? That just seems really unnecessary.
I think it's supposed to be more efficient. Instead of creating six origins and than after the player picks one he won't see much of the others for the whole playthrough (like in Dao) you can choose one, and the others appear in game.
The problem I have with it is that it makes party interaction really restricted compared to other games of that type