That's a pretty far cry from "complexity is unavoidable". Reading that to me implies that the complexity is inherent in programming language design, whereas this follow-up argument seems to say that complexity is the result of tacking on new features.

The latter is a bit tautological, since the size of the language grammar is itself a measure of complexity.

I think they even haven't adopted newer JVM features, it is a hosted language designed to depend on its host, plus it is a Lisp.

The complexity would be to grow like Common Lisp, instead it is up to Clojure folks to write Java, C#, JavaScript code, therein lies the complexity.