Yes, command line suffers from discoverability of which different applications (such as ln/mklink) may not be consistent.
It is one of the bigger problems (imho) of the cli but it doesn't go against GPs point.
The command line does have a learning curve (partly because of the above), but it is also quite rewarding.
The cli excels because it is extremely flexible, with far more options available than a set of buttons could ever display. But discoverability rounds down to 0, and there are footguns. It seems like spreadsheet software has found an almost drop in ui that would greatly enhance the cli.
It's a 3 part problem: available commands, their options, their syntax. Part one would need to capture prompt input before enter was hit using solutions similar to those found at [1] perhaps the most useful but least complete one there is the one that uses apropos so something like `apropos -s 1 '' | sort | grep calc | less`. Similar solutions would be required for two and three. The roughest and easiest prototype would probably be two tabs in a split screen view, which would allow for selection of displayed matches to then modify the prompt creating those matches in the other tab. But Calc style popups directly attached to your cursor would be more useful still.
[1] https://stackoverflow.com/questions/948008/linux-command-to-...