If you read the original article, the use of WebAssembly is mainly across a broad array of device types where it will be packaged into an app. That app will require installation, accepting permissions, and all of that just like a native app.
The point is moot except for anyone watching Prime Video in the web browser.
The WebAssembly component gets pulled on app startup. That means you make a bug fix, deploy a new build to an S3 bucket and every single user is running the fix inside of ~24 hours.
The point is moot except for anyone watching Prime Video in the web browser.