> I could a bit biased because I do have prior experience with SML

You're probably under-weighing this factor.

The average programmer looks at SML syntax and cannot make, pardon the expression if you will, heads or tails of it.

Indeed, I'd argue the average programmer still considers recursion an advanced topic.

Recursion. Very interesting. My daughter didn’t know much about programming, then started CS. The first semester language was Ocaml and they of course used recursion quite heavily and she’d didn’t know it was supposed to be complicated. The second semester had assembly, C and Java and suddenly it was a problem. I had to remind her that she’s had already done it in the first semester.