See I think it depends on the role. If you're hiring a css oriented front-end developer, that's fine. If you're brining in my JS architecture oriented folks, the kind who are more adept at setting up a babel rc than a keyframe, well then it's unfair.
I will agree that these tests can be overly domain specific, but I also think that the desire to have engineers with great breadth of knowledge is a good one.
I'm with you, breadth of knowledge is important. That is certainly what my role demands of me and I like it, but in being broad I think we sacrifice depth in some of these categories. I think this particular test is incredibly general and is well suited to many full stack developers, I agree with the author that extending it to a sockets implementation would make it even more fun.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.