If you are writing massive software to handle comprehensive control for an aircraft carrier, you'd better be writing it in loosely-coupled components with well-defined interfaces, or its going to be a maintainability nightmare no matter the language features.

If you are doing that, Scala's flexibility lets you, internal to each component, take the approach most suitable for the team responsible for that component addressing that components requirements.

I can see where Scala's flexibility could make a bad situation worse if you are writing an enormous piece of software but not doing it in loosely coupled components but instead doing a tightly coupled nightmare -- the OO equivalent of spaghetti code -- but, even though it might be less of a disaster, that's still going to be disaster in Java or C#, too.