You're probably right that the presentation here is misleading. Most common things like arrays, dictionaries, sets, and more don't really present any trouble in practice. You only use the techniques in my article when structuring your program more broadly, and arrays were just an example.

I'll make a note that for arrays specifically, someone took the trouble to make a mutable version that's usable in IO. Nobody would ever read and write references to an immutable version over using just MArray, but my post might mislead them into doing just that.