My experience of pair programming is the opposite. In a pair I get maybe 4x as much done as when working alone.
Mostly it's because when we hit a point where one person would get stuck, the other usually knows what to do, and we sail through almost anything with little friction.
Maybe the multiplier is 4x and by the time you have a team of ten you're back down to 2x? My theory is a bit of a hyperbole and I don't know what the multipliers would be? But I know that many times you can move quick when you're small.
And to your point, a single person can easily get stuck, I know that applies to me many times.
There's that but youre missing a lot of variables. E.g. if one of you had perfect sleep and the other didn't the individual with perfect sleep will perform better for longer.
I don't get why people try to simplify - you're removing important details that determine performance and therefore output. This leads to false conclusions.