This is your very limited personal experience, not an empirical study on the matter.
That said, I can agree in part, in that integrating everything and make optimal use and insights from various Psychological Testing/Tests is difficult and requires great attention to detail, psychometric knowledge/competence, history, psychosocial environment, and knowledge of psychopathology. Thus, not surprisingly, it is very easy to not be great at it in terms of it being super helpful or additive.
I don't really know what all this secretiveness from psychologists is about? I mean, there are certainly some limits about sharing raw test data with non-psychologists or psychotherapy session notes if the patient has not signed a release....but alot of what you seem to be speaking about doesn't seem kosher. So, again, not sure what is happening there?