Interesting that you should mention it. This talk https://www.youtube.com/watch?v=mVVNJKv9esE mentions some arguments why a DSL would not be a good approach for frontend/JS build tools. Namely that a DSL isn't adequate if the underlying best practices or requirements change a lot. That's why operating at a higher level of abstraction (function chaining/piping/composition) would make more sense.

Now... that doesn't really favor Webpack. And I still don't quite understand why that tool is so popular.