It doesn't matter which success metric is used, the point still stands. If you only measure the ratio of solo-founder companies that are successful, you haven't measured anything at all about how likely a solo-founder company is to succeed. We need to know how many of each type failed as well.
This is not scientifically sound without the full data, you are right. But I don't think that is the point. If you had all the data and parsed it.. and it told you that as a solo founder you had a 21% chance to exit, and as a group founder you had a 23% chance to exit.. so should you do a group founding as your next project despite not knowing anyone to found with?
I don't think it works like that. Some people naturally do better solo. Some people already have a group on a hot idea. I think you should go with what is working. What the point of this story is, in my mind, is to say "look - a lot of articles say solo founders are bad. Here is some data that it isn't that bad, and perhaps solo founding is a valid way to run a business"
