For the coders, geeks, nerds (whatever the preference) GUI is not necessary. For the other 95% of the population that want things easy and pretty to look at, a nice GUI is an absolute necessity. If not, we would still be using DRDOS, MSDOS, CP/M, FORTRAN... those were the days.
I agree with you 100%
Thats the main reason many took so long to even try Linux.
Much still has to be done from the CLI.
Many just want point and click control and set up.
A simple typo and the whole set up can get messed up.
The beauty of Linux on a Raspberry Pi is you can take an image of your SD card (15 minutes work) and throw whatever commands or changes you desire at the OS and if it breaks the system all you need do is to restore that image you took earlier (another 15 minutes work) and you're back to a perfectly working system.
You have the added advantage of having a mini server tucked away from sight without a screen, a mouse or a keyboard hanging off it that, when required can be accessed at any time either on site or off site. And of course you have the advantage of a unit that will not draw more than 2ah of power yet can control most if not all of your home automation needs.
I think the choice of Windows over Linux goes a lot further than choices of GUI over command line usage. Commercial and economic drivers I would imagine have played a big role in OS choices over the years. This is beginning to shift dramatically and particularly over the last five years. Development in the ARM processor world has really thrown down the gauntlet to the opposition and Microsoft and Intel are no longer the giant they once were. I liken this to the battle between iOS and Android.