Different methods of therapy appear to be equally effective despite having theoretical foundations which are conflicting with each other. The common aspect between different therapies seems to be "having someone to talk to", so I'm inclined to believe that really is what's behind the success.
If you are fortunate, you have people like that in your immediate circle, but increasingly few people do.
A big part of therapy is also rapport. Many people go through many therapist before finding one that works for them. In part, you can think of this as the market performing the assessment your'e referring to.