Windows filenames "like to present a convincing façade of being UTF-16" in the exact same way unix filenames "like to present a convincing façade of being UTF-8". Both are common assumptions neither is actually true, and all of that is well-documented.

> unix filenames "like to present a convincing façade of being UTF-8"

Except they never have? Unix paths have always been bags of bytes, both before Unicode and UTF-8 were invented and after. It's just convention that modern Unix systems use UTF-8 as the text encoding for paths.

> Except they never have?

And neither have Windows paths ever actually pretended to be UTF-16, that's my point.

I would express it more as "programmers in Unix environments like to act as if everything still uses the C locale everywhere, all the time".