Ignoring a learning curve for the sake of argument, the most effective UI's tend to be command-oriented. If you memorize the abbreviated commands, you don't have to traverse menu trees. Command-line interfaces can still have menus for newbies.

For example, pressing Enter or giving the command "m" or the fuller "menu" at the command prompt may give a menu similar to:

   1 - Search for employees (SE)
   2 - New hire (NH)
   3 - Department transfer (DT)
   4 - Etc.
   0 - Back to prior menu [app-wide convention]
   Command: __

Here newbies just enter menu numbers; but next to each menu is a shortcut command, such as "DT". After they get experienced, they start using the shortcut commands to jump across the menu tree as needed, they are usually global. It's like a Go-to (gasp!). The prior stuff is still on the screen for reference because they wouldn't get a menu when using the shortcut commands; it only shows up if you ask for one.

And the shortcuts may take optional parameters, such as "SE gar" to search for all employees with a last name starting with "Gar". (Without the parameter, they get a typical search form.)

Before GUI's, I worked with users directly to gradually fine-tune such gizmos, and after a while their productivity screamed. They loved me and even forgave my lack-luster people skills.

Many emacs modes use something akin to this (see magit as a stellar example). This makes learning it relatively easy (it's discoverable), but becoming a power user is still possible.

Yup. Magit is a stellar example of UI that's both discoverable and ergonomic. It shows you a popup with a list of options available to you at a given stage, with plainly visible keyboard shortcut. But it doesn't block or slow you down with this.

Say you're trying to show git log. The first time around, you'll press "?" to show the top-level popup, notice "l" is for logging, press "l", see the popup for logging commands, notice you need to press "l" again, press it. The next time around, you'll just press "l l" without thinking, and Magit will react as fast as you can type.