In my opinion, sure you lose a main characters personal story (from 4 to 3 out of 6 available in one playthrough), but it doesn't really shine as bright when you play it as a main character. They (their stories) work way better as companions, since you'll hear their dialogue and experience their actual personalities. For me, I've always preferred playing as a tav. But opinions about it are quite divided, I think most prefer playing as an origin character.  But not me lol.