I think this is kind of misleading. Yes s-expressions have very simple syntax in and of themselves. But s-expressions are not all that's required to get all the control structures in Clojure. You need to memorize all the special forms and all the standard macros that people use on a day to day basis. And they're just as hard (actually IME harder) to memorize as any other syntax. let, cond, record, if, condp, let-if, fn, def, defn, loop, recur, if-some, when-let, for, ->, ->>, as->>, cond-> ...

To this day I have to look up whenever I get back into clojure what the "syntax" is of ns, require, import, etc.