I agree that the final version of this concept will need to be simple enough to be conveyed in a few lines, with more of the lines left to explore character as you said. It all has to flow from one thought to another, as if Kylo were really saying these things in the heat of the moment, so it can’t feel like he’s giving her a college lecture about cloning or complex family lineages or introducing new terms halfway through the last film. And we need to be aware of Rey’s reactions as well. When she says ‘No!’ as she is on the verge of tears, it can’t be to something like ‘Actually Rey, your parents were good people.’ This always felt weird, since surely she would want that to be true and she wouldn’t fight back against it.

So yes, I agree with you RL that Rey’s parents being retonned as good is a strange thing that feels like a fanedit in the original film, a replacement for information that was originally much more devastating to Rey. Unless we can recreate that moment, the scene will always feel off.