I don’t think promising to finish what Vader started is going to appeal to Rey that much.
That’s the point. She wants to take Ben’s hand, not Kylo Ren’s hand. Even after everything he’s learned, he’s still pushing his same old perspective. If we make his offer too reasonable, the audience won’t like that she doesn’t accept it. This has always bugged me about Ascendant v4. With the removal of “And take the throne”, it desperately needs a line like “And take his fleet” to make it clear his intentions are still sinister while wanting Palpatine to die.
EDIT: Also worth considering that we’re going to be modifying their prior conversation so Kylo is focusing on how alike she is to Vader, anyhow. Most of their prior conversation takes place with Vader’s mask looming behind them. It makes sense narratively to include such a reference.
Oh, and like I said, there’s no way to seamlessly edit around “He (Palpatine) killed my mother and my father” so we have to include them in some way.