Perhaps that's because such a setup is not viable period. To me, the whole idea of trying to combine more than one type of vehicle in one (e.g. a "spaceplane", a tilt-rotor, a "flying car", a half-track etc) is that you end up with something that combines most of the DISadvantages of both with only a few of the advantages. In this example the "orbiter" still has wings, some kind of landing gear, some sort of an aerodynamic control system for re-entry, none of which it needs at any time OTHER than re-entry. It also has to carry all the "spaceship stuff" which it does not need during the re-entry. In other words, at any given time in the mission, good half the mass of the vehicle is dead weight that's sitting there doing nothing, but still has to be carried. Is this not the very definition of inefficiency? It's hard enough to build a good airplane or a good spaceship, but to build something that's both is, in my opinion, well-nigh impossible.
Not sure what you're getting at -
all vehicles contain some level of compromise to maximize their usefulness. A commercial jetliner carries around landing gear, flaps, brakes, etc. which make up a significant portion of the aircraft mass but are worthless for 95% of the flight. But the aircraft itself is worthless if it can't takeoff or land.
A spacecraft that can't re-enter and slow for landing is similarly of very limited value.
The Space X landable booster has to carry considerable extra weight for the landing struts and fuel in order to soft land - but the alternative is for the entire booster to be disposable. Isn't a single use spacecraft the
real definition of inefficiency?