Both hypotheses in this case are plausible. Beyond that, it would be great to have the tools to numerically calculate a psychological phenomenon such as the placebo effect the way a physicist calculates the energy of a particle. But we're very far from having them, and in the meantime, I don't know of a practical alternative to RCTs that would expand our knowledge at least as much. (I think we can both agree that over-reliance on significance testing is a problem, though not one limited to RCTs.)