Has anybody found some Psychotherapies seem logically inconsistent?

I was reading about some of the philosophies behind certain psychological interventions. And I find some of them what appears to be illogical. Im not against therapy at all im just questioning the hidden assumptions in them.

Am I right to assume it’s impossible to really test any therapy and call it empirically backed? How can you do a double blind study on mindfullness ? I like my Popperian severe testing.   Acceptance and commitment therapy and cognitive behavior therapy presumes the feelings behind anxiety and depression are caused by thoughts by outside stimuli that causes emotional states. Isn’t this Deterministic and leaves out Neurology, automatic body function and circumstance ? It seems to be unfalsifiable. If it works good! If someone isn’t improving instead of questing the assumptions of these therapies  it’s put back on the patient saying that they need to change the way they think.  Furthermore it seems to confound the symptoms as the actual cause. 

Why should I accept the premise that emotional states are caused by thoughts ?  If I drink 10 cups of coffee I’ll have severe anxiety and then have negative thinking patterns. Am I overthinking this ?