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.
it's a bit more complicated than that
https://www.youtube.com/watch?v=Z37i8-FnAh8
and on top of this the method of therapy is to find better copings, not just to vent.