It probably isn't. The initial public release of Clojure was in the fall of 2007. Scott Burson has been working on FSet since at least 2004. He himself says it's inspired by Refine.

I stand corrected. I still maintain my point about (idiomatic) Clojure being terribly slow though.

And terribly beautiful ;)

Just personal preference and enjoy programming in it. Programmers give too much importance to programming languages.

Clojure can be made to run very fast (it compiles to the same bytecode as Java after all) for the hot paths at the cost at writing less idiomatic Clojure.