That’s the same for everything, no? I assume most JavaScript websites come packaged with their (transpiled, minified) versions of the “standard library” of what

That’s the same for everything, no? I assume most JavaScript websites come packaged with their (transpiled, minified) versions of the “standard library” of whatever framework they’re using. And that has to be transmitted as gzipped bundles of plaintext javascript. Further, tree shaking is much harder with a dynamic language. My understanding is that a WebAssembly implementation would usually be smaller than a JavaScript one, assuming you’re using a language without a runtime.