It's useful if you want array-like semantics (e.g. O(1) lookup) on Unicode text strings, because you have a fixed size for every codepoint, unliked UTF-8. Python for example uses it internally.
I think that's the issue here. People disagree on how useful or not useful it is. It's maybe not ideal, but I don't think it's anywhere near so bad as to be entirely not useful. Strings-are-sequences-of-bytes is worse in my opinion. Python literally used to have that. It was worse.
The problem with what Python used to have is that the encoding wasn’t fixed.
I’ll agree with you that strings-are-sequences-of-bytes is bad. That’s painful compiler-flag, codepage, &c. territory.
But what’s not bad is strings-are-sequences-of-code-units. That’s what Rust has, for example. Rust strings aren’t sequences of bytes, but of UTF-8 code units, and the two are semantically very different.
