Maybe in the far future, but in the near- and medium- term the same backwards compatibility that you believe (a little unfairly, I think) has hobbled Javascript

Maybe in the far future, but in the near- and medium- term the same backwards compatibility that you believe (a little unfairly, I think) has hobbled Javascript will keep it dominant. If existing web applications can't be bothered to update to support ES6 or Typescript, what will make them rewrite in Web Assembly? New applications will, maybe, but it's a very, very slow change, with so many opportunities for new events to change the conclusion.