I'm wondering if you missed my argument entirely. Why aren't you saying "I'm sure that if a greater percentage of successful businesses are started by white dudes , there must be a good reason for it"? Looking at the demographics of success stories is actually not at all helpful. In fact it would only be helpful if an equal number of startups began as 1 founder vs 2. Otherwise this data tells us nothing.
Let's look at this from a different perspective. Assume that the data conclusively shows that 2-founder startups have a higher chance of success than 1-founder startups, by a huge margin (say 10x). Does that mean that you should seek a co-founder before launching your startup? Even then, it does not. Consider two different startup ideas, one is founded on a very solid plan with a good chance of success, the other is founded on a bad plan with a lot more risk. The good plan is going to have a much easier time of finding a co-founder, because the potential co-founder will look at the idea and see that it has a lot of merit and potential and they'll be enthusiastic about joining in, whereas the bad idea will have a much harder time finding co-founders. However, imagine if someone with a bad startup idea pushes much, much harder to get a co-founder because they have learned that startups with co-founders are more likely to be successful. Will that help the company's prospects any or will it just warp the equation and result in a bad company failing even with a co-founder?
I think it's more important to go about a startup with your head screwed on straight than to attempt to imitate the forms of previous success. If you find someone you trust who seems to be a valuable addition to your startup as a co-founder, then by all means make that partnership. But if you can't find a co-founder for whatever reason but you are still quite convinced of your business plan then I don't think you should wait. You should certainly be careful that you aren't deluding yourself and be sensitive to any criticism of your startup idea nonetheless, but a good plan is a good plan even if you go it alone.
