I'm not really arguing that Clojure code is "truly" difficult to understand, if that is taken to mean reasoning about its performance and effects. Rather, I'm talking about the fact that idiomatic Clojure code encourages writing functions upon functions upon functions, which continually builds up layers of abstraction that inherently make code more and more difficult to read. Example:
console.log("Hiya.");
console.log("How's it ");
console.log("going?");
vs.
printFirstString();
printSecondString();
printThirdString();
function printFirstString() { ...etc }