Doing a data transfer "does not" cause a CPU to be
A very narrow data path with limited memory causes
the process to be slow but the processor is doing
VERY little work.
The data path is the restriction. Doing massive copying
on a network of twisted pair is both slow and silly.
Most any tape drive made in the last 10 years is
much faster than a "network transfer".
Your comments on the speed of older machines shows a
real lack of experience in these computers.