Whether or not an individual requires solitude depends entirely on the person. Some people feel their flow is interrupted in the presence of others while some are invigorated by working with others. Though the creative process varies from person to person, I often look to William Wordsworth when considering creativity.
Wordsworth was one of the great nineteenth century British Romantics. He believed that poetry came from the spontaneous overflow of emotion recollected in tranquility. I think you could apply this to many forms of art. Creativity requires at least some form of contemplation, which is a process that takes place privately. For some, the actual work is further enhanced by the participation of others.