The study looks at crashes where vehicles collide which are within 500lbs in weight of each other. It does not say much about crashes where the vehicles are farther apart, for example a 5000lb SUV striking a 3500lb car. In cases like those, injuries and deaths are still going to be lopsided, with the occupants of the lighter vehicle suffering more damage.
This chart from IIHS is telling, it shows how heavier vehicles tend to have higher partner death rates than lighter ones.
At the end of the day, a larger, heavier vehicle is still safer, for the people riding in it. But not necessarily for the others on the road.