> pattern matching without the ability to check for exhaustiveness defeats the safety they provide

This holds for a lot of C# vs F# issues... There is a fundamental difference between "it's valid, but our tooling hides it from us" and "the execution environment guarantees that it can never happen".

The single pass compiler, functional foundation, currying syntax, and other features that provide guarantees simply can't be replaced with equally robust syntactical sugar. Much in the same way that writing imperative programs that follow OOP principles in possible, but will never give you the system level guarantees that a compiled class sytem will.