[Mvandenbergh]

Not to mention the complexity inherent in getting the engines separated from the rest of the vehicle.

Also, they're at totally different places along the technological readiness curve. They're proposing a theoretical concept, SpaceX has already recovered two first stages. Even if their parachute concept was theoretically superior (which I don't think it is) by the time they got it working, SpaceX would have years of operational experience with hoverslam.