The default should be a clutter for new users, and the customization option should be make the UI customizable by hiding things you won't ever touch because you use shortcut keys.

The other way around is yeah, hostile. But of course it looks sleek and minimalistic!

On the early iPhones, they had to figure out how to move icons around. Their answer was, hold one of the icons down until they all start wiggling, that means you've entered the "rearrange icons" mode... Geezus christ, how intuitive. Having a button on screen, which when pressed offers a description of the mode you've entered would be user-friendly, but I get the lack of appeal, for me it would feel so clunky and like it's UI design from the 80's.