If you have a project that one person can do in their head, that is fine--no need for cooperation, a team, or even a process approach. But in general, most professional Web developers are in situations where projects are big and success needs to be reliable. I think a person with no training and no cooperation with others could produce a fantastic Web site. But I think Web developers can be trained to do a better job more reliably with a documented, process approach in which tasks and products of those tasks are systematically identified.