It is, that's the point. Reason is, as was said upthread, a "veneer". It changes the syntax only, nothing else is different (you can convert back and forth between the syntaxes losslessly). TypeScript makes deep changes to the language by adding type safety.

I have no idea how you got that from my post. I don’t know whether type safety is “a fundamental part of a language” or not, but that’s irrelevant to my point. TS extends the JS syntax to support type safety. Reason changes OCaml’s syntax altogether because it’s broken. Big difference.