The research done for the original Macintosh UI showed that keyboard users aren’t actually faster than mouse users, but think they are because they lose track of time while concentrating.

Do you have a link? I suspect there's some asterisks there. I used to operate a photo minilab and could process a roll's worth of photos in 1-2 minutes. That's 4 seconds at the outside to evaluate a photo, make brightness and color corrections, next photo. No way I'd be able to sustain the same rate by having to mouse around and click at least four different targets, bouncing from brightness to magenta/green to blue/yellow back to magenta/green to cyan/red before giving brightness a final tweak. Fitt's Law[1] is death to speed for all sorts of workflows.

I'm not saying that keyboard-based operation is superior in all cases, but a good keyboard-centric interface can eliminate the need to acquire a target (e.g. menu/toolbar item) for the most common operations because there's a hotkey. Well-understood operations can go almost at the speed of thought (either the operator's or the machine's).

[1] https://en.wikipedia.org/wiki/Fitts%27s_law

Thanks for the link. Unfortunately without any details on the experiment design it's hard for us to get anything out of it. What was the task, who were the participants, what was their familiarity with the software they were being tested on?

I can say that this talk of using the keyboard being so fascinating that it takes up significant mental resources to be not represent my experience using and seeing others use keyboard-centric interfaces. When I use magit, or when I was operating the minilab I mentioned above, I don't have to think about what key to press to do the thing I want. I am in fact "so disengaged [with the mechanics of manipulating the interface] that [I] have been able to continue thinking about the task they are trying to accomplish". Competitive StarCraft is another example that illustrates the same point without relying on personal anecdote.