I read that the problem of DoS2 was that custom character was less interresting to play than origin's because they had no background.
That's a kind of "glass half empty" observation.
A more fair observation is that Origin characters were "more interesting."
In BG3 it looks they're trying to lead custom character to a higher level.
I'm glad that they are doing this. If I was them, I'd focus less on "Origin Characters/Companions" and more on "Origin Classes" and "Origin Races" that have the same depth and story integration of their current origin characters but with more space to feel like you are injecting your custom character into the roles. Even though you may have some history or circumstances that you're somewhat beholden to, at least people would be calling you by *your* name and you'd feel a little less obligated to "do what X would do" etc. In DOS2 you could always do something "out of character" if you were playing an Origin character, but then you were kind of knee-capping one of the benefits of having the origin character to begin with (i.e. a more fleshed out character that heightens the suspension of disbelief because they feel more "real" within the context of the game and story.)
So what's left for origin characters exept that you can experience a character that was created by someone else and give you a few different options during the whole game ?
Origin characters do offer developers a depth of integration that your typical custom characters simply won't allow for. My first experience with a multi-player DOS2 play-though had 3 origin characters and 1 custom character. The custom character played a female lizard enchanter. And, honestly, I feel like they missed out on being brought into the story as deeply as the other players because their character *wasn't* as integrated into into it. Cool, interesting and unique things were happening with every else.
However, they could have taken 95% of Red Prince's storyline and applied it to anyone who was going to play a custom lizard character. The same goes for just about any of the origin characters in DOS2 (who were, principally, race based because it uses a fairly classless system.)
We'll see what Larian does going forward, but it does seem like they recognize that they need to make custom characters a lot more interesting.