The criticism is that a martial artist or scientist is actually trying to attain a highly specific brain-state in which neurons have particular patterns in them; a feeling of emptiness, even if part of this brain state, is itself a neural pattern and certainly does not correspond to the absence of a mind.

The zeroth virtue or void - insofar as we believe in it - corresponds to particular mode of thinking; it's certainly not an absence of mind. Emptiness, no-mind, the Void of Musashi, all these things are modes of thinking, not the absence of any sort of reified spiritual substance. See also the fallacy of the ideal ghost of perfect emptiness in philosophy.