Counting up the number of people who could've written a given non-anonymous paper is pretty unheard of in academia afaik. The answer is usually politely assumed to be "exactly the number of authors". I've certainly never seen this behavior. So I'm not sure your answer is actually at all clarifying.

Probably, and this is just a guess, neither Simons or Sullivan claim they could've written the paper alone. And it's certainly impossible to write essentially the same paper without plagiarizing. So probably there are either zero or two people who meet the "could've written this paper" criteria.

So, why didn't you just say "there are more than zero/two billionaires who read HN"? Seems less round-about.