Im not of the opinion that we've found the "best" user interface. I think the biggest hurdle is that "best" is so different to different people. One part is familiarity, as many power users know, your setup would be utterly useless to an unfamiliar person. I guess the current paradigm is a local maxima of the convergence of discoverability and efficiency and still working on our diverse device specifications (display sizes, input devices and performance).