I've heard that said, but I don't see how it's a big deal. OK, the very first example introducing let bindings would have to come with a sentence like "the 'in' part of 'let ... in' means 'in' just like in English: 'let' the binding be valid 'in' what follows". You don't have to define a whole new syntax where a single sentence in a language tutorial might be enough.

But I admit that I probably can't fully appreciate whether this is really difficult for someone used to JavaScript.