This right here.

I'm taking his results with a pound of salt. There's no detail, so the experiment cannot be reproduced by a third party. Where's the scripts and WASM programs used for testing so that others can verify not just the results, but that the WASM and JavaScript programs were actually comparable.

Yeah, and it also doesn't go into questions like what kind of tasks the code performs. For example, if it is constantly copying huge arrays back and forth the bottleneck is memory, not computation.

I recall a recent blog post by Mozilla where they said they removed most of the overhead in JS <-> WASM.

I agree, without data, the observations cannot be replicated or discussed. I'm sure there's a simple explanation for each point.