Let's say that it's scientifically proven that ghosts exist. Would they then stop being supernatural and become natural, thus making it impossible to ever have proof of the supernatural?
I'll compare to the concept of human culture being called superorganic, which is an old cultural anthropology concept which can provide a model for critical thinking. We don't understand culture, yet we define it, record it, measure it. Hard to predict, I'll admit. Refering to it as superorganic implies it exists at a higher complexity than we understand. Gravity and many other observational phenomena also exist at a higher compexity than we understand. Thus although you may not like to refer to such things as supernatural, it's not wrong, it's an opinion.