Usable means an interface which is (i) consistent and (ii) well suited to the task at hand. It does not mean you should not require any training nor that you should be able to intuit the functionality without looking at the manual.
vim is an example of software that is both highly usable and intended for use by advanced users.
> I spent all of university using vim purely as a way to indent and colour my code; but intelligently using splits, buffers, tabs, code folding, ctags etc should not require luck to discover and exacting patience to use.
You're doing it wrong. Read the bloody manual.