C is the king of raw performance, there's no denying that. But for the vast majority of high-level, user-facing applications today it's a bad fit.
Clojure is more than fast enough for serious server side programming, often coming close to Java in performance with minimum amount of tuning needed in the average case. When you add multithreading into the mix, it's not even a contest; the amount of time you'll have to spend to make an idiomatic Java or C++ run both correctly and fast is gargantuan compared to a language where concurrency was built-in from the start.
Clojure is more than fast enough for serious server side programming, often coming close to Java in performance with minimum amount of tuning needed in the average case. When you add multithreading into the mix, it's not even a contest; the amount of time you'll have to spend to make an idiomatic Java or C++ run both correctly and fast is gargantuan compared to a language where concurrency was built-in from the start.