What seems more likely to me is that the "decompressing a large number of small ...

flashman on Dec 9, 2016 | parent | context | favorite | on: The Finder’s GUI tax can be very expensive

What seems more likely to me is that the "decompressing a large number of small archives" task is so rare that Apple hasn't optimised it. More likely than "Apple added an arbitrary delay to make the interface more satisfying."