FYI, I find the conversation fruitful! The criticism is much appreciated, and readers will do well to hear your counter arguments.

I very much agree with your points, especially that "billable hours" is not the point, that expediency or rarity of talent can easily be more important.

A fuller, more accurate treatment of the concept has to include that. Perhaps it's still useful for folks to (sometimes!) think about optimizing the person/hour, since that is of course an important part of the equation, and optimizing it does help.