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 techn

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.