The data isn't well-presented (52.3% of exits would be a negative if 68% of the companies considered had only 1 founder, as that would mean less received an exit than would be expected), but if you normalize the percentage of exits with the percentage funded, you roughly see that the author's original claim is likely true.

1: 52.3 / 45.9 = 1.1394

2: 30.1 / 31.9 = -1.0598

3: 12.5 / 15.0 = -1.2000

4: 3.7 / 5.3 = -1.4324

5: 1.4 / 1.9 = -1.3571

Maybe the idea is that a single founder situation is preferred, but as creating a startup can be stressful, trying, and involved, maybe doing so with a single partner (that complements your skillset) is a compromise?

I had never considered creating a business with a partner/co-founder. There would just be too many issues. People have a difficult time understanding what I'm trying to do even when I explain it in plain English, so I shudder to think what it would be like if I were doing something completely new/groundbreaking/different.

I can't deal with someone nagging, draining, or getting in the way as I try to do what I'm doing. It's always been fairly clear to me that the route I should take is to found a company solo, then bootstrap it to profitability, while keeping the employee count low (43-73, or 259-585). Then not go public. That is, I should avoid dealing with a co-founder, investors, or the overhead/inefficiency/bureaucracy/politics that comes with having more than a certain number of employees.

Also, it became clear (especially in the world today with so many service-oriented companies to contract out to) that it's entirely possible to do almost anything with 42+me employees (which is the "ideal" number of employees (1 CEO/founder + 6 leads/executives/managers + 6 individual contributors per lead/manager/executive), as there's only one layer of "management").