For the example I gave, unless the hunks were asymetrically distributed, `git add -p` would require pressing "n" 20 times to skip through the excluded hunks (among other things), even when the user could visually see all the hunks, and know which ones they wanted. Where as gui would only require the clicks to select the "y" hunks.
I realize this is arguing a difference in the efficiency, not capability, of the UIs; but that's basically my point. The use-cases where one or the other is optimal are too closely situated together in the problem space to say one is inherently the better choice, even for VCS tasks.
While command line interaction may allow the user to receive a whole screen's worth of information at once, it forces them to interact with it in a serial fashion, regardless of whether out-of-order interaction with on-screen elements would allow them to complete the task faster.