> The sad truth is that the status quo for GUIs is absolutely terrible, and most were rushed out and not properly tested to check if they're really usable without a mouse.

This is the key point. No platform UI paradigm focuses on keyboard navigability and speed, all focus on mouse and visual effects for discoverability in a pursuit to dumb down the user experience enough to make it usable for everyone, breaking power users in the process (and increasingly also accessibility stacks).

Yes, but GUIs are by default mouse driven, very rarely one can see a keyboard driven one (I haven't seen any).

And TUIs are only keyboard driven. So the choice for speed if you don't need graphics is always - TUI (or CLI).

A GUI requires a lot more work to be keyboard-driven and as fast as a TUI.