Good UI is based on input type, mouse or touch input UI is not best for gamepad input. If x1 UI was well designed it would be gamepad centric (note, this would not take away anything from voice control)
For the rest we'll have to agree to disagree that the Xbox One UI isn't well designed.
What I do think is inane is that people think the Xbox One voice controls only seem more efficient because the UI isn't designed well for a controller.
I've already shown an example, where Voice Controls can be and are more efficient than the most efficient controller based input possible. The single button push to accomplish a task.
The example, being the ability to push the Xbox Button in order to return to the home page from wherever you happen to be. There you have the following two situations.
The button press is as fast or slightly faster than issuing the voice command of "Xbox, Go Home"
if the controller is already powered on and in your hands.
The button press is slower, and sometimes significantly slower than issuing the voice command if the controller isn't already in your hands or is powered off to conserve battery life.
You cannot get more efficient or faster than a single button press to accomplish a task, and yet even then, at best it is similar in speed to issuing the voice command to accomplish the same task. And at its worse, controller off and not immediately at hand (like when watching a movie), significantly slower and less efficient than issuing the voice command.
That means that no matter how well designed the UI is with regards to a controller control scheme it will always be inferior or at best similar in speed and efficiency to issuing voice commands.
The lone caveat here being that it is true only as long as the system can process and execute your voice commands reliably and quickly. But that has nothing to do with how well the UI is designed with regards to controlling it with a console controller.
Of course, there are things where controller input is more appropriate or accurate. Sustained movement and the ability to stop at an arbitrary point, for example. Like continuous scrolling on a web page. But for things like that you also have gesture based controls.
And, of course, an argument could be made that some of the voice commands aren't as well designed as they could be. Volume up and volume down could arguably not be as good as say, volume [x] percent if you need to adjust volume by a large degree, but again the UI design has no bearing on that anyway.
And this is true not only for the Xbox One, but for the PS4 as well for the limited number of voice commands available (assuming they didn't bork their voice command implementation) and minus the gesture controls.
Regards,
SB