Rust is fine as a low-level systems programming language. It's a huge improvement over C and (because memory safety) a decent improvement over C++. However, most applications don't need a low-level systems programming language, and trying to shoehorn one where it doesn't belong just leads to sadness without commensurate benefit. Rust does not

* automatically make your program fast;

* eliminate memory leaks;

* eliminate deadlocks; or

* enforce your logical invariants for you.

Sometimes people mention that independent of performance and safety, Rust's pattern-matching and its traits system allow them to express logic in a clean way at least partially checked at compile time. And that's true! But other languages also have powerful type systems and expressive syntax, and these other languages don't pay the complexity penalty inherent in combining safety and manual memory management because they use automatic memory management instead --- and for the better, since the vast majority of programs out there don't need manual memory management.

I mean, sure, you can Arc<Box<Whatever>> many of your problems away, but that point, your global reference counting just becomes a crude form of manual garbage collection. You'd be better off with a finely-tuned garbage collector instead --- one like Unity (via the CLR and Mono) has.

And you're not really giving anything up this way either. If you have some compute kernel that's a bottleneck, thanks to easy FFIs these high-level languages have, you can just write that one bit of code in a lower-level language without bringing systems consideration to your whole program.