Try spending a week using just ed, mail, and curl. Those are actual command-line programs, not just terminal-based programs. The litmus test is whether they would work with a real paper teletype.
"When I log into my Xenix system with my 110 baud teletype, both vi and Emacs
are just too damn slow. They print useless messages like, ‘C-h for help’ and
‘“foo” File is read only’. So I use the editor that doesn't waste my VALUABLE time.
Ed, man! !man ed"
The real challenge these days is javascript. I'm not aware of a text-mode browser that interprets javascript.
I'd also like to give a plug for w3m. It's far more user-friendly than lynx, and IMO more advanced than elinks.
I think we can be more purist still: menu-driven UIs are not really command line either. MH has a truly command-line UI for mail, while the mail program doesn't.
Some years back, I spent a couple of days trying to use ed for some serious text preparation work before I decided this was not the kind of experiment one should do when better tools are available and real work needs to be done. Using nmh (an MH reimplementation) used to be a pleasure, until its clumsy handling of HTML (quite a bit worse than mutt) began to overwhelm the whole user experience.
I'd say the keyboard-centricness still separates them from, say, Eclipse.