Facebook's Go engine is not remotely close to competing with AlphaGo. In fact, it's about comparable to the pre-existing top Go programs; the only newsworthy thing about it is that it's from Facebook and it uses neural nets.

Since AlphaGo's architecture was published in nature, wouldn't it be somewhat straightforward to reproduce something similar to it given the resources of Facebook and an already existing team of people tackling Go? I would expect other Go software to quickly follow in AlphaGo's footsteps and then build on it, perhaps surpass it by adding some different optimizations.