In this context, Luke is saying that Leia knew Rey has a good spirit and heart because their bond was stronger than blood. I don’t think it is a non-sequitur.
Luke’s basically saying, “Leia saws those dark vision of you too, but she trained you anyway, because she saw your true spirit. She knew the real you, because your bond was stronger than blood.” That’s the idea at least.
Hmm, I get what you mean now, maybe there’s a line to be made that could get that idea across.