Most knowledge about human computer interfaces was obtained through metrics. Groupings, menu bars, corner buttons, context menu orderings, and other things didn't just spawn into existence. There was a time where human pattern recognition and physiology was an active consideration for user interfaces. One of the reasons mouse input became popular is precisely because interfaces were created to be easy to use with it.

All of this brings me to my questions: Why do you reject measuring how good an interface is? Or given your dismay over keyboard based workflows, why do you think they would win most of the time?

I'd wager that if actually tested, in only a few scenarios the keyboard would win, while hybrids (with both mouse and keyboard input) perform best for most people.