At present, I have only one example of an unbearable truth that follows from these fields - the Weber–Fechner law [1]. It seems that this single law is the origin of a brand new mental discipline called Psychophysics which has given us cool things like some lossy digital formats - but it seems that Psychophysics is not even close to the Medicine I am asking about.
If not using all kinds of euphemism, my question could be read like this "Are all psych medical workers just a scammers?" but of course that's not the level of harshness that I want to establish, because mental professionals have some amazing skills to make some bullies the loser in a discussion. It's just that I have a feeling that these specialists are not from a discipline that I can trust, but I have no facts other than the well-known crisis of replication in psychology and medical research [2].
So let me formulate a friendlier version of the question: is it worth trusting any psych* specialist if all their knowledge come from unreliable sources like astrological-fashioned theories of interpersonal compatibility, and all their methods seem to be aimed at fooling around like a Scientology's E-meter based polygraph? I once used to cheat a lie detector in an interview to cover up some issues that I don't want my boss to know about, so after such a success, I will never go back to believing in mind-based fields of "scientific" knowledge unless there are really strong arguments.
[1] https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law
[2] https://en.wikipedia.org/wiki/Replication_crisis