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.

It helps that for most cli tools, any incorrect usage will show the usage text, including --help

You also have to just know what program to invoke with the —help arg.

Good luck guessing ‘grep’ from first principles.