Facebook succeeded through luck, timing, hard work and good engineering
You're talking about a social network which was not the first, not the biggest and had some serious competition in its inception. Luck, timing and good engineering only go so far when your competition had the same luck, timing and good engineering. The way I remember history Facebook evolved through a careful strategy to take over markets as it went and by the time it was released to the general public it was a long way behind an incumbent competitor.
Sure timing has a bit to do with it (e.g. the now laughable Google+ may have been a hit in 2003) but your comment implied that it was a simple idea and it just needed some massaging to get to an otherwise empty market. That's pretty far from the truth.
Facebook may not have been visionary, but it certainly was the product of a great strategy. Also we like to talk about Zuckerberg as Facebook alone without realising all the other work that is going on. AI research, communication systems, network design, contributions to open source projects for really large scale systems, etc. They are at a forefront of machine learning and computer vision, datacentre design, and more recently VR.
To claim that he just built a social network through luck and a bit of sweat on PHP is just garbage.