Rangers win the deal, but Canucks do okay IMO. Miller had a NMC, so it was either stay in Vancouver or go to NYR. That's what trade protection is for, and why he signed long term for $8M instead walking to UFA or getting moved as a rental.
Vancouver also saves $3.5M in cap, got some trade capital, and Mancini must be someone they think has some upside. NYR improve (unless Miller is legit a cancer, then who knows) and Canucks get immediately worse on paper, at least until they convert the 1st and spend that cap. And I guess if the fog lifts for Pettersson.