Really, almost any GC'ed language out there is a better pick for this sort of task (except the ones that are poorly designed for this, like Go).
You speak of "unnecessary complexity" like the complexity was just pulled out of thin air for the purpose of making Rust harder; no, the complexity is inherent to building a functioning application, the difference is whether it lives in your head or it lives in the compiler. Personally I'd rather the compiler handle things like bookkeeping, moving memory around, checking that the types and cardinalities are right, and ensuring errors are handled rather than repeatedly having to debug those things at runtime in an extremely slow and punishing feedback loop.
Its necessary for system programming, and as we can see people talk about it whenever C++, C, OSes, Browsers, Games, etc.. are being talked about because it works really well in those domains.
But when you are building a UI, C#, Kotlin, Swift, Typescript and even Java are much more productive with good speed, safe (even safer than Rust), and with language constructions that map really well to this domain.
Rust achieved a very good set of features, but unfortunately the price is its complexity, which is a burden you don't need to take when you are creating UI's.
Sure you and i (im mostly a C++ dev) can use it to make UI's, but unless you are creating something really complex that needs every drop of performance and memory, like big Games or a Photoshop, you don't need this productivity and HR tax(its much harder to find people in C++ and Rust) that languages like Rust and C++ ask of you.
There's no such a thing as one language to rule them all, and Rust will not the best candidate for domains it was not designed for. Swift for instance is much better at this and with a very good performance, where it would also be a good fit for a Photoshop clone or a browser.
Rust will make a great UI language once the ecosystem has matured and async has gotten polished more. If upgrading the "Webpack" of the future meant just resolving compiler errors, we would be in a much better world. Same goes for upgrading dependencies on the frontend, which at my company becomes a blocker every 2 weeks or so due to the NPM security advisories being released, accompanied by the total lack of visibility into the dependencies' interplay that the Node ecosystem gives you.
In my case i'm comparing it with languages that are also powerful, safe, fast and more well designed for this kind of scenario, which JavaScript or Python aren't.
But if i had just two picks, between JavaScript or Rust, of course i would choose Rust without blinking. But once there is more options.. (in this case you can read my comments above).
And i agree with you, that if you sum it all, maybe you get more productive (as in ready to ship) in Rust than with JavaScript.
C# - requires an obscure runtime (Mono) on most platforms
Kotlin - suffers from JVM's infamous GC pauses and startup time
Swift - not open source (not SwiftUI, the good part)
TypeScript - mostly same problems as JavaScript
Java - same problems as Kotlin
No one has managed to do open source cross-platform development well yet IMO. I'd be happy to be proven wrong.
F#: https://safe-stack.github.io
To watch:
Kotlin NATIVE
Scala NATIVE
Note that even with Scala's complexity, the language's focus is first and foremost domain modelling & expressiveness.
Rust is first and foremost, a language for memory safety and raw performance, it just happens to have some level of expressiveness. Nothing wrong with that either.