You're overestimating the difficulty of Facebook by over a factor of 50. Not to mention similar systems already existed. In fact, this is the first time I remember someone claiming that actually building the FB initial product was challenging (versus timing, acting on the idea, marketing, etc.)

Edit: parent comment was saying it's so much easier to with work with inexperienced people, and that an experienced "corporate" dev couldn't make Facebook if all the screens were given to them.