I think this would be very situational even in the case of WASM. Without needing a garbage collector and using only a JS buffer for message handling and DOM up

I think this would be very situational even in the case of WASM. Without needing a garbage collector and using only a JS buffer for message handling and DOM updates, for a long running application, there might be performance gains that would be hard to directly measure. With simple examples, the JS will generally win handedly. But for more complex apps that use more / increasing memory and perform involved state manipulation, I’m willing to bet you’d see the favor slip. This manifests as a snappier experience with less / no GC pauses and a clearer dev experience with a better separation between domains. Rust is just a better language to work with, so it has a certain future-proof quality to it that would pay dividends long term compared to JS in any case.