I too agree with Bingowings about keeping the scene and brings up some good points, especially since Ben needs to finish the story he started. (and lied about at the beginning.)

Also, during the duel between Luke and Vader, it was Vader reading Luke he learned about Leia being his dauther/Luke’s sister. Or at least that’s how its portrayed.

It resonates with Vader and the kiddos. Vader didn’t feel a connection to Luke until Palp revealed Luke being his son.

So it seems like Vader has no connection to his offspring until someone either tells him. It could be because he wasn’t there for their birth … Maybe Palp is using his power to “shield” his connection to them, until he found Luke to be powerful and could be turned … or any other reasons.

So taking away Obi-wan’s reveal and making it Vader telling him about his sister kind of goes against the grain on what’s already been shown/established.