One major point missed by this article is motivation — with a team of founders, drive to work is very high. You have someone else to interact with, work with, and keep you on task. I've found that working on projects solo, it's a lot easier to "fall off the wagon", so to speak — get distracted working on the wrong things, working without feedback, or stop working at all. This obviously differs from person to person, but it's one of the reasons why I believe more in a team rather than a single founder.