The reason I don't buy it is because two average people can get married and have a happy family life simply by cooperating. Cooperating is not enough to succeed with a startup, they must also have a good enough idea, good execution of the idea, and some luck. Often nothing short of brilliant execution of the idea will make a startup work. And they probably need exceptional people, not average people.
Another thing is that a happy startup life, most of the time, is unsustainable. People at the startup can be happy and get along with each other right until they run out of funding. I've watched it happen. They often still get along after they've stopped working on it, but the startup has failed.
In a lot of ways other people can negatively impact your creative process by being a distraction. But at the same time, if you find someone where you can happily communicate with then maybe the ideas can pour out.