WebAssembly is expected to be around a long time, so it's not enough to just measure its speed today, because engines aren't very mature yet. As engines mature, it will likely get faster.
Also, performance is just one factor. Other criteria include security model, standards and governance, Web integration, nondeterminism.
Also, performance is just one factor. Other criteria include security model, standards and governance, Web integration, nondeterminism.