Besides, when colleagues of mine decided to demystify the command line and learn it proper, they're always surprised how much easier it is than they expected.
The GUI/CLI gap, as far as I have seen, is one of willingness to invest some time to learn.
That's not true, CLI programs would still exist even if they could not be composed. And I would guess that if you counted how many of our commands include 1, 2, or 3 executables, the 1 column would be the biggest by far.
One of the major headaches of CLI programs is that they're hard to learn interactively because there's no starting point. You have to read the docs. The point of a GUI command builder is that it gives you something interactive to play with to start to learn how the CLI commands work. The point is not to do everything through the builder, the point is to bootstrap people to the point where they no longer need it.
Also, there's no reason a GUI command builder couldn't also show you how to do composition.