Comment by jason_oster

> and had to run glue code to copy things in and out of Webassembly memory.

Not surprising. The FFI boundary is always a bottleneck. If you can eliminate it, you will see where the WASM JIT shines. You have far more control over mechanical sympathy with C/WASM than JavaScript (though far from perfect).

Also, consider publishing your findings and ask for reviews for optimization opportunities.