First of all they are using Slick 1. And yes, they are missing important optimizations. They are not-precompiling queries, which means the Slick Scala-to-SQL compiler has to run again and again for every query. Slick 1 only supported precompiled read-queries. Slick 2 added pre-compiled write-queries. http://slick.typesafe.com/doc/2.0.1/queries.html#compiled-queries
I created a PR upgrading it to Slick 2 and optimized queries. https://github.com/TechEmpower/FrameworkBenchmarks/pull/824