For my master thesis I did a lot of digging into the research on success factors for startups. And at least based on what I found back then, you're right. The correlation is weak between any factor like this and success. Generally positive though, so it does make sense to try doing some planning. But it's definitely not a requirement.

In general, observable factors doesn't strongly correlate with success. Probably both because there are so many to choose from and because the real world is complex and typically doesn't align well with any predefined plan.

This kind of analysis sounds far more interesting than a lot of the "just do what I did!" startup writing that's out there. Do you have any recommendations for further reading from this perspective?