Your objection is addressed in the comment. See "If you're a materialist, you might object..."

That's the wrong level of description. It adds little to the argument about whether neurochemistry or perception underly the efficacy of psychedelic treatments. As a counterpoint - human cognition and perception only exist in contexts beyond the brain - a perceived world, brain development through perceptual stimulation, language acquisition etc. Brain in a vat does nothing.

Missing the point completely …

The issue is that not all chemical processes produce transcendence.