I don't know, to me $9B seems like a lot of money for a glorified IRC client built on web tech. Sure, you don't pay for the tech, but in the end you can do a lot with that kind of money. Elon Musk sold his first two businesses to get the funds to start what he really wanted to do.

We don't know where Oculus would be without FB, i would argue they are better off because they are creating a new market and are in a capital intensive business. The VR market is still slow overall. Without FB, they could have already run out of breath or cut corners on the product.