Moreover, non of the problems with the origin system are new. All the problems that are in Bg3 were present in DOS2 and it seems like Larian decided they aren't big enough to scrap the system
That's the thing though. This over-reliance on the systems of a previous game in an entirely different series speaks to a lack of faith in their skills as a developer. It's not the most encouraging thing for people to observe.
I would definitely argue that the origin system is absolutely not a core defining reason to DOS2's success. It absolutely isn't when actual praise for the system is rare, and most of the community outright encourages you to play as an origin character instead of custom because the custom option is missing a lot of context exclusive to each character, and written so awkwardly and poorly in comparison.
People did make great use of the origin system, but probably not for the reasons they think. Considering how Larian keeps talking about focusing their design based on data gained from analytics, it'd be a case study on how analytics without the context is misleading at best.
I doubt they will get rid of it completely, seeing how much time and effort has already gone into content that is only available when you play the origin characters (dreams of Astarion of his master, uniquie dialog options for each origin, etc)
There's no reason that Astarion dream cutscene can't just be a shared dream that you can observe via tadpole powers, and especially even something you can probably stumble into seeing if you are romancing him. I feel like trying to encourage replayability of an 80+ hour cRPG through things like locking exclusive cutscenes behind your choice of main character and the highly implied removal of companions not in your active party after a certain point is a foolhardy endeavor, and outright hostile from a player choice/freedom standpoint. The latter was at least tolerable from a gameplay standpoint in DOS2 because builds were a lot more free-form there, so you weren't affected in combat at all, in a game largely all about the combat.
Here, with the bigger focus on the writing and everyone having specific classes, adapting the same design and expecting it to work out somehow just feels cynical as hell.