Comment by the_mungler

Not really. How would you test a rocket engine at low atmospheric pressure? You can't exactly stick a rocket engine in a vacuum chamber and light it. Then once you're launching something into space, you may as well have a first stage to go along with it. Are you saying they should have launched the booster stage by itself? Why? What would they learn from that? Would you ever expect them to launch a booster on it's own in practice?