I agree with the people who says that playing a custom character should offer as much content as an origin character. So custom character should have and story arc, quests and custom dialogs like the origins.

right now, it seems, they are working hard on the origin stories, while not doing the same on the custom ones. After all, the dream person an scenes would probably happen anyway if you play an origin character. So it is not an special story arc for custom characters, just the main plot.

And neither can we imagine a PC story and play as that PC because the choices and dialog options we are offered are bland and more limited than the ones open to origin characters. For exaple, if you play a wizard with the dame intelligence (or more) than Gale, you can't even tell him to stop explaining things you already know and being so condescending. You can't compete with him to be the clever one. You are shoehorned into playing dumb so Gale seems "clever". Similar things happen with the other origin NPC's. The way they are writen, your MC can't really answer back. You are never allowed to have the last word. And sometimes, you can't even have a word. So the solution to "just imagine a background and personality" begs the question, why play then? why not just write a fanfic or an original story?

While resources are limited, they promised that playing a custom character would be as rewarding as playing an origin character. So if they won't offer a personal story arc and oportunities to, basicaly, get the uper hand on the companions, they are failing.

Example: with the goblins you can throw the shit to the face. Or you can force them to kiss your feet. It is writen that way, because you are agains an NPC. And, basically, the writer can imagine that dialog with you playing one of their origin charaters. since they want origin characters to shine, they allow to have the uper hand. Now compare with conversations with the origin characters. Why can't you answer back to Shadow heart? All of them can be snarky with you, and at no point would you have a chance to tell them "I am benching you because you keep insulting me". Or because you are unable to work with the team, etc. In a real pen and paper game, you could say that. So no, the "blank slate" remain blank in game because custom characters aren't really considered as an equaly valid choice. Otherwise, we would already have that.

And yes, conversations with the companions, could be used to talk about your own past and personality so you can define your custom character better. If not by choosing a backstory, by offering broader choices and having reactions about them in the short and long term. Choices only offered to the custom characters, because those are the ones that need to be defined by said choices.