Nope, the placebo effect can have physical effects and be genuinely curative. The level to which this is the case is highly variable from patient to patient, but it is inaccurate to say that is limited to improving sensation and perception of illness. Not to mention, in many cases the malady being treated is one of perception, for example, in pain management. And alleviating pain in itself has downstream positive effects on disease progression and patient QOL.