I personally think that in a healthy therapeutic relationship both therapist and client have equal but very different power.

The fact that there is a very significant difference between the two in what regards self-disclosure (and normally also in what regards knowledge of psychology, psychotherapy, several cases, etc), grants the therapist more power. This is a power to understand the other in the context of their life story, a power to explicitly know the client and help him/her change, a power to be more in control of own emotions and reactions during sessions, to be the more stable person that the client usually needs (ideally and at least for the duration of the sessions), to contain the client's emotions and experiences. I think most clients need their therapist to be at least somewhat more powerful than themselves in these ways, because otherwise the therapist may not seem credible or any more helpful than a trusted friend.

On the other hand, I also think the client needs to be the more powerful of the two when it comes to choosing where to next, how far and how fast, how much or how little to be involved in the therapy process at different times, whether or not to continue therapy, whether or not an intervention is useful to the client or if maybe the client prefers somewhat of a different approach. Without this, the therapy would become more about the therapist than the client. So I think the client is the only one with the power to truly know him/herself and the power to change. (Of course, therapists can also change, but no therapist can change the client - only the client can do that).

So I really think that the therapeutic process is co-created and the people involved need to have the same amount of power so that it doesn't become an exploitative relationship, but at the same time it needs to be d ifferent forms of power so that it doesn't become a power play or a friendship.