I agree, authors whole "The time has come to re-evaluate terminal and command line interfaces." is weird, if anything we should be moving MORE towards terminal and command line usage.

Another example from recent history, I just wanted a easy way to mount all connected drives, so whipped up:

    lsblk -l | grep -i part | cut -d " " -f 1 | xargs -I{} sudo mount -m /dev/{} /mnt/{} # automount_all

How would you even approach this with a GUI? You'd need something like Automator or whatever is called on macOS, then manually pipe GUI elements together (or some other way?), and finally there is no automated way of actually testing that it works, so once it breaks because the inevitable OS upgrade, you'll need to manually fix it. Then whatever solution you came up with or used, is almost never reusable for other things.

Meanwhile, a shell alias/function just sits there, easy to see what it does, can control anything in your computer, GUI or not (one way or another), lets you build up your own "database" of tools that all compose together (again one way or another) and finally is easy to put under automated testing.