Really not convincing that you know what you're talking about if you're taking the DCX prototypes flying up to 3km as meaning that we had landing orbital class boosters sorted out in 1991. That was a hopper vehicle comparable to the original SpaceX Grasshopper prototype.
An orbital class booster isn't a booster that goes to orbit, it's a booster that is part of an orbital rocket stack.
The important distinction is that the DC-X prototype was, at best, supersonic given the low altitude and flight time record, while any efficient booster powering an orbital spaceflight is easily going hypersonic by the time it's returning to Earth.
