But that acknowledgement would itself lend Searle's argument credence because much of the brain = computer thesis depends on a fundamental premise that both brains and digital computers realize computation under the same physical constraints; the "physical substrate" doesn't matter (and that there is necessarily nothing special about biophysical systems beyond computational or resource complexity) (the same thinking by the way, leads to arguments that an abacus and a computer are essentially "the same"—really at root these are all fallacies of unwarranted/extremist abstraction/reductionism)

The history of the brain computer equation idea is fascinating and incredibly shaky. Basically a couple of cyberneticists posed a brain = computer analogy back in the 50s with wildly little justification and everyone just ran with it anyway and very few people (Searle is one of those few) have actually challenged it.