I agree with you, as far as adding new features to C# from F#. When I have the time to refactor larger codebases, I'm often finding new C# features/syntax makes the code easier to understand and reason about (often due to decreasing the number of lines needed to accomplish the same thing, without overcomplicating things). I do make sure that if I'm introducing new language features, that I'm refactoring related portions of code, so I'm not leaving behind the "old" way of doing things while also introducing the "new" way for the same functionality. I'm always thinking of the next developer with anger issues coming into the codebase after me.
