Mass 3D printing an item that can already be manufactured through e.g. injection moulding or assembling standardised parts is never going to be efficient at scale. That's not what it's for. Where 3D printing excels is at producing one-offs or short runs, immediate production (no time consuming buildout phase manufacturing moulds and setting up production lines), on-site or mobile manufacturing, or making designs that are not amenable to traditional manufacturing processes such as objects with complex geometries or internal voids.