Why’s it easier to cut the origami shot? The dream comes out much more cleanly, and the origami shot still has meaning without the dream (Gaff is telling Deckard that escaping with Rachel is just a fantasy that can never be real). The dream, on the other hand, means nothing without the origami shot at the end.
Deckard falling for Rachel is being a unrealistic and unicorn nicely represents that. But this can apply to both the origami and the dream. The difference is that the dream would imply that Deckard himself subconsciously knows it, while with origami, Gaff is relying that fact to him. So, the dream can stand on its own just as easily.