Yes, for many or even most of us, scientific method is the way to prove what works and we take meds that work based on clinical trials for efficacy and safety.
However, the placebo effect, which is what you’re referring to when you talk about true believers, is a known effect of some treatments and has its own validity. Placebos can be efficacious in many situations. While I don’t believe and would not benefit, there are many who do and western medical science takes it seriously.
Please note that I’m not advocating here – not in the least. But for some kinds of ailments, pain, in particular, placebos work.
Again, I’m not advocating the use of magnets for anything or anyone.