The remaining piece of the puzzle is that Lihaoyi's libraries and general approach is exactly what a joe average coder would want. There is minimal use of advanced features, it is all quite straightforward and simple.
There are other productive contributors in Scala, but among them I would rate Lihaoyi to be among the least "magical". The fact that he is both practical and productive is what makes him unique. I guess my point was that there is a lot to be learned from that. For some nice examples of what it looks like in practice see his series of blogposts titled "how to work with x in scala".
Some context for people who have limited knowledge of Scala.
Lihaoyi is one of the most prolific coder's, not just in Scala, but in any language. He looks like he is much to humble and modest to claim so himself, so I will do it for him.
Discussions on Scala on HN tends to contain a somewhat large volume of comments that explicitly or implicitly tries to communicate that Scala is a language that is much to complicated to really be productive in. Lihaoyi is a rather clear example of why this is not true. If this random internet citizens endorsement doesn't convince you maybe the book will :)
SQL is designed for rows of flat data. GraphQL is designed for nested data. It's two very different use cases. Trying to say one is better than the other completely misses the point.
Loving the lyrics :D