That has nothing to do with discoverability. Discoverability isn't about "guessing" it's about being able to see it.
Discoverability in CLI is --help. But you can't discover you have to use --help. So CLI is always fundamentally worse than GUI.
You also have to just know what program to invoke with the —help arg.
Good luck guessing ‘grep’ from first principles.
It helps that for most cli tools, any incorrect usage will show the usage text, including --help