I'm not implying exhaustiveness is always necessary, I'm saying if you want feedback from the compiler to support a type-driven extend-refactor workflow that is

I'm not implying exhaustiveness is always necessary, I'm saying if you want feedback from the compiler to support a type-driven extend-refactor workflow that is commensurate with inheritance-based typechecking, as is one of the major arguments for inheritance and subclassing to work they way it does in a static language, then you need exhaustivess to deliver the guarantees and maintainability experience if pattern matching is to replace inheritance+sublassing. Dynlangs here do not apply.