The Finder’s GUI tax can be very expensive
I wonder whether this is not an example of a UI interaction which is slow on purpose, to emphasize how much work the OS is doing for you.TaxAct and TurboTax, for example, both operate on (in the typical case) kilobyte scale data requiring trivial math.  They also make both saving the data and calculating taxes take 5+ wall-clock seconds when they actually require milliseconds and nanoseconds respectively.  This is largely because (non-technical) users don't trust your computer did the math right if the answer comes back instantly.  (I also suspect there is an element of "Wait if it is so easy to calculate my taxes why am I paying you to do that.")