But this also runs in the browser. Using HTML and Javascript. Except now it's done slightly differently in a way that's easier for browsers to optimize, if done well.

WebAssembly and Rust may be massive overkill for most web applications, but so is React or Vue or whatever Javascript framework is popular these days. When the inevitable rewrite happens, we might as well enjoy the benefits of the new, faster-than-the-old-evolved-moloch web UI.

If anything the move from the old system (React+WebAssembly) to the new one (Rust+minimal JS+WebAssembly) will make the web application itself smaller and easier to grasp.