I am not confident in my ability to declare what parts of the brain serve no optimization purpose. I should clarify that by 'optimization' here I do mean the definition "make things somewhat better" for an arbitrary 'better' (this is the future volume compression remarked on earlier) rather than the "choose the absolute best option."

I think that for an arbitrary better, rather than a subjective better, this statement becomes tautological. You simply find the futures created by the system we're calling a "mind" and declare them High Utility Futures simply by virtue of the fact that the system brought them about.

(And admittedly, humans have been using cui bono conspiracy-reasoning without actually considering what other people really value for thousands of years now.)

If we want to speak non-tautologically, then I maintain my objection that very little in psychology or subjective experience indicates a belief that the mind as such or as a whole has an optimization function, rather than intelligence having an optimization function as a particularly high-level adaptation that steps in when my other available adaptations prove insufficient for execution in a given context.