Well, a major difference is that you can discover a GUI and find solutions organically, while the shell is pretty useless without prior knowledge. Even as an experienced user, you need to know to put research into those issues.

I usually struggle with GUIs and I find the concept of discoverability awful. Having to randomly click through tons of menus until you discover the right place is frustrating. I use MS Word maybe twice a month, and every time I go through that ritual of clicking through several tabs just to be able to discover how to save a file. If I used it more often I certainly would remember, but then it's no longer about discovering.

Oh and if you're lucky you have the option to hover for a second to find what the icons mean through a tooltip. Having to do that with every icon until you find the right one is not pleasant.

I just find typing "help" or "man" a lot more intuitive than the random clicking on icons.

I'm sure that I'm a rare specimen and most people would prefer clicking to reading, but personally I find discoverability a bad user experience.

There's nothing wrong with the concept of discoverability. Having the capability of discovering how to do thing X without referring to documentation is fine. The problem is when users are forced to rely on it because the documentation is trash or nonexistent. That does seem to be a trend and I share your frustration with it, but discoverability and good documentation can (and should) coexist.

Yes, you are right that discoverability isn't detrimental unless it becomes an expectation that this is how one must engage with software. I assume that it is also the preferred way to engage with software for some people .

Good user interface/software design is good regardless of whether it is graphical or not though.

Having a row of icons with vague meanings, or endlessly nested/badly categories menus isn't intuitive or easy.

Conversely, there are a plethora of terminal-based programs with absolutely excellent UX.

Anyone can edit a well-documented template/example config file, and a good CLI program is almost like an interactive conversation, which again is an extremely intuitive experience. It's not the fault of whether the interface is graphical or not in most cases, it's just mediocre/bad software.