Actually, this isn't quite true. Close, but the languages do have a few differing features.
Your main point is a little questionable - sure, there are languages very similar to C# (Nemerle, J#, etc.), but then you've got F#, P# (Prolog), IronScheme, IronPython, IronRuby... I mean, the existence of the DLR itself kinda puts holes in your argument (for some of the above languages).
Claiming "yeah, but the F# team did everything" is somewhat true (as they did for the first release), but it's not a meaningful complaint. That's going to be the case for virtually any new paradigmatic language being put onto a general-purpose (i.e., procedural, object-oriented) programming framework. The Clojure team had to do everything to make it work on the JVM, too. And in current releases of .NET, more and more of that is being pulled into .NET core and being leveraged by C#.
Your main point is a little questionable - sure, there are languages very similar to C# (Nemerle, J#, etc.), but then you've got F#, P# (Prolog), IronScheme, IronPython, IronRuby... I mean, the existence of the DLR itself kinda puts holes in your argument (for some of the above languages).
Claiming "yeah, but the F# team did everything" is somewhat true (as they did for the first release), but it's not a meaningful complaint. That's going to be the case for virtually any new paradigmatic language being put onto a general-purpose (i.e., procedural, object-oriented) programming framework. The Clojure team had to do everything to make it work on the JVM, too. And in current releases of .NET, more and more of that is being pulled into .NET core and being leveraged by C#.