I'm not sure what you are looking for. Isn't your question akin to asking since Java just compiles to bytecode, what advantage is there to writing java instead of bytecode.

The higher level abstractions that are directly supported by Scala are precisely what make it more "scalable" from an authoring perspective. In particular, the amount of help it provides in writing many objects to support an OO design along with the functional support it has go a long way to reducing your code down to quickly communicating the abstractions you are using, and not the language used to describe them.

This is particularly true in a method body, where one can use inference to remove the types from the code rather well. With judicious use of map/etc, often changing the collection type you are using is reduced to a single change in the code, and not through every intermediate collection along the way.