The origin-custom character debate is an interesting one. I was working on an RPG where it was a mix. It was a headache to design it because i did not want to make compromises between the two system but wanted to make it as logical as possible. How it worked is you had to create a party of 5 custom characters, defining their race, stats, proficiencies (system was classless) and even their personality and interests using a similar Tag-system what Larian used in DOS2 and then the game offered logical origin stories and motivations/goals for your character (based on choices you made earlier). It also allowed to pick non-so-logical goals/origins as well, only exclude motivations which would not make sense for your char at all (as an example origin stories were usually not tied to birth location, skills or race, only in some rare cases where an origin story made sense only at a certain location in the world or by being a certain race or having a certain skill). These specific Origins & Goals/Motivations eventually would have led to personal quests and conflicts with each other's journey potentially, but the good thing was they were tied to custom choices as minimal as possible and they only opened optional dialogue/quest choices. There was a amnesiac origin story for characters who did not want to pick any origins/goals for their character - to balance that with XP they had a "need to find out how i am" questline where eventually the player was able to define who their character was before (and get the same amount of XP they would get with specific origin quests). Also, to make the game accessable there was a separate generate button where the game automatically applied a logical backstory from the list to my char created, so it gave the player preset characters basically.
Dialogue choices I designed like in Kingmaker, all kind of choices to be available and based on what you pick your initial personality (tags) either got stronger or shifted during the story. The party members also reacted to the things you said. They had an initial attitude towards you based on your race/skills/origin/equipment but that you were able to shift by picking certain dialogue choices affecting their attitude towards you the good way.
Though the project died I was quite happy with the character creator, it even generated a short texted Backstory to your journal, trying to tie the choices you picked during char creation in a logical way (similar to how Realms Beyond tied the distribution of your attribute points to your backstory) and i managed to make the initial party conversations to feel personal and sound logical despite this sandbox system.
All in all, what im trying to say is that i think a hybrid system could work, you can design appealing origin stories first and take the choices led to that origin story apart and make them separate customizable choices as possible and then allow the player to customize them basically as they wish (to a certain extent) and the companions to react to these. This is not easy and the toughest part is to only enable logical connections between these, but I do believe it can be made if designed carefully if this is planned from the start. I secretly hope Larian thought about this when they started to design their origin chars and their story/dialogue design process (especially as they do cinematics which are harder to redesign once they are set in stone) and eventually we will be able to customize our characters around these backstories as much as possible and have the best of both worlds maybe? Just my two cents.