> Rust does not have a global system cache for libraries, and I don't think there is any package manager installing pre-compiled Rust libraries, so at least for the initial compiles, Rust needs to do much more work than C, for Rust dependencies at least.

FWIW, Nix can do this (via Carnix). But it turns out not to be too useful anyway, because any feature flags that you use will invalidate the cache for everything that depends (transitively) on that crate.