Except maybe a safer code. JavaScript, even in the most able hands, is treacherous. I consider myself as a cautious, careful developer but I have been bitten several times by JavaScript's eagerness to give sense even to the most basic typo's ("hey, great! An additional variable!" whereas it's just a typo by the developer).

TypeScript is already a step in a better direction, despite all its shortcomings.

Producing WASM files from stricter/safer language is, for me, a good enough reason to use WASM.

For the rest, I mostly agree with your standpoint (complementarity, ...)