JITs may approach native performance in theory - but the battery consumption and memory consumption are not very good. ("Better than JS" is a low bar).
As hardware becomes stronger, I would like to do more with it, and when it comes to portable devices, I want more battery life. Nothing justifies compiling same code again and again, or downloading pages again and again like "web apps" shit.
I understand where developer productivity argument comes from. But we can have both efficiency and developer productivity - it is a problem with webshit-grade stacks that are used today that you can't have both.
I personally think flutter model is future. You need not strive for "build once - run anywhere". You can write once and build anywhere a cross platform HLL and that's better.
As for sandboxing, maybe it is that your OS sucks (I say this as linux user); Android / iOS have sandboxing with native code. You shouldn't need to waste energy and RAM for security. IMO enforcing W^X along with permission based sandboxing is better than webassembly bullshit that is pushed.
And webassembly itself seems to be a rudimentary project with over ambitious goals. JS bridge being so slow and not having GC support ("To be designed" state) make it unusable for many purpose. Outside HN echo chamber, not many web people want to write in rust or even C++.
Without WebAssembly I wouldn't have been able to ship 2 products pro-bono within intensive care units and operating theatres directly helping with COVID.
I understand your dislike towards WebAssembly (albeit Web stack trends / flavour of the month esque development). I am not the largest fan of modern web development. Nevertheless love for WebAssembly is not due to developer productivity. After shipping 20+ WebAssembly products (alongside native counterparts) I am yet to meet an Engineer who enjoyed the WebAssembly/Emscripten/Blazor pipeline. However what WebAssembly has achieved for me is: Do people use your app? and within certain markets it allowed me to grow, do good, and say yes. This is the only real reason why someone should go down this route.
Wasm is like the JVM or CLR in that regard. It's not the future - it's the past.