Webassembly doesn't solve the same problems as styleable components, scoped CSS, and things like that though. Webassembly solves the problem of "how do I deploy this software that isn't written in Javascript to the browser client?".
Sure, it also is sorta about performance, but JS interpreters are actually shockingly fast in the modern world. Mostly wasm is about moving your existing C++ code (or whatever) for your existing formats or algorithms or tools into a web/mobile client without having to hire someone to recode it all in TypeScript or whatever. That's not sexy, but it's valuable.
I think webassembly actually acts as a reliable target when building software. Every platform will have a fast web assembly runtime. So you just build for it and you can deploy for any platform mobile or desktop.
Sure, it also is sorta about performance, but JS interpreters are actually shockingly fast in the modern world. Mostly wasm is about moving your existing C++ code (or whatever) for your existing formats or algorithms or tools into a web/mobile client without having to hire someone to recode it all in TypeScript or whatever. That's not sexy, but it's valuable.