I believe the ketamine anti-depressant experiments use a different anesthetic to put subjects under in order to split the trip experience from the lower-level chemical effects, and still find benefits. If the trip itself is not necessary for ketamine, that makes it more plausible that it's not necessary for psilocybin etc.

(Of course, this doesn't rule out the possibility that much of the benefit is coming from after the trip during regular life based on experiencing regular life with 'reset' neurons under the Carhart-Harris/Nutt interpretation.)