Could the positive benefits just be a placebo?

It's certainly a possibility that the positive effects of microdosing may be a placebo; however, it doesn't necessarily undermine the legitimacy of those effects. Placebos are an inert substance that can induce real physiological and psychological effects resulting from one’s beliefs and expectations for improvement. So, if individuals experience benefits to their well-being from microdosing, then it remains a valuable practice, whether the effects are pharmacological or caused by the power of belief.