Another consideration here is that you can use languages that offer control over data layout as a natural feature, which can matter a lot for good cache utilization etc. In many cases the data layout matters a lot for performance.

You can do this in JS too with TypedArray and whatnot but the key word here is 'natural.'

I've been working on a game engine as a side project with C++ and WASM -- and there are already many improvements over what I was getting with JS due to less GC, better data layout (the data layout thing is also esp. helpful for managing buffers that you drop into the GPU). I don't think it was about 'pure compute' as much as these things. C++ and Rust give you tools to manage deterministic resource utilization automatically which really helps.

A bonus is that the game runs with the same code on native desktop and mobile.