That argument makes sense when we're talking about languages that improve productivity at the cost of efficiency, but consider that we are now talking specifically about code already written in a compiled language. There is no need to run say, libpng, in a virtual machine outside the browser.
You could upload wasm to npm and distribute code like that, no need to compile it on target machine. While node.js generally does not have problems with that I've seen missing tools/MS Build on Windows machines.
