Further, there is an immense value in GUI based systems: discoverability. On a GUI, you can learn how to use a program without ever consulting a manual just by inspecting your screen. This addition is what brought the computer to the masses.
Finally, the terminal model of UNIX is just horrible. The hacks-on-top-of-hacks that are needed to turn the equivalent of a line-printer into something like nCurses or tMux are horrible. The current terminal is like this purely because of legacy. If you'd design a system for
"working in terminals, with strings of text and non-binary-format config files" from the bottom up, it would look totally different. Sadly, getting it to work with existing software would be a total nightmare.
All that being said, UNIX still has the better terminal (though I hear good things about powershell). Certainly, it is the best system for "working in terminals, with strings of text and non-binary-format config files". Though competition is sparse (windows, and maybe mac, depending on whether you consider it to still be unix or not).
Man and apropos get you a long way.
The near ubiquity of --help as a flag helps too.
Well managed program distributions will even tell your shell how to tab-complete what it wants.
MOST CRUCIALLY, though, the text of a command line or config snippet can be pasted, emailed, im'ed, blogged, and found with a search engine! Try describing how to navigate through a moderately complex gui in text or by phone... it's a disaster.
passwd is not read every system call and anything that is read frequently is almost certainly in the fs cache.
I got about 3 assertions into the article before I decided I had enough of that bullshit.
If there were performance problems, something would be done. And you can easily switch to LDAP or your backend of preference.