It seems to me you're blaming the general problems of discernment on psychotherapy. This might be a good time to recall your "causes aren't correlations" training and incorporate it into your analysis of the relationship between psychotherapy and practice. Psychotherapists have been "harming" (cf. your Dr. Britton reference) people for years, long before several of them co-opted "mindfulness" to attract more clients.
The problem is neither Buddhist nor psychotherapeutic. The problem is dukkha/samsara. There are crappy therapists and crappy meditation teachers and a whole lot of messed up people in the world. "Adversities" will happen. Identifying causes in this mess, as the Buddha duly noted, is merely academic. In the Buddha's sense, then, the "dark night" is much more banal than most of us want to admit. It's not a special occurrence at some so called "stage" on the Path. Perhaps this stems for your belief that the purpose of meditation is to become enlightened? For that, I'd recommend some good doses of Ajahn Sumedho.
The Buddha didn't teach that life is suffering or that the self is a dream. As Thanissaro (Hang on to Your Ego et al) points out, the Buddha taught you need a healthy ego (Thanissaro also, to my surprise, generally speaks highly of psychotherapy as a beneficial supplement to practice). The Buddha didn't eradicate all his senses of self. The Buddha taught what is not self, not that there is no self. He taught us to see our senses of selves for what they are: inconstant (anicca) aggregates (khanda).
Christian Mysticism and practice, are in my opinion, incompatible. I love St. John of the Cross, but Uniting my SOUL with GOD is not part of any Buddhist practice I'm aware of.
Also, you've not addressed the problems inherent in psychotherapeutic classifications/taxonomies/diagnosis tools themselves. Psychopathology is itself culturally bound. Realities like death, old age, sickness, disease transcend cultural boundaries.