I don't agree at all. The author only considers short term productivity and does not acknowledge the long term benefits of the skill sharing.

Let's make up a metric, du (dev units), for how much a developer produces in a day, and let's say an average developer produces 100du per day.

If we have two developers, Sally and Frank, producing 120du and 70du respectively. Short term, for these two people to pair program, the production of the pair programming has to be greater than or equal to 190du.

But if we instead consider how productivity increase as experience grow, perhaps the next day, Frank will produce 80du and Sally 121du, then this is definitely worth it long term.

I would agree with the author if the question was "ONLY pair programming" vs "ONLY individual programming", but that is a stupid question.