Could you give an example package you'd prefer to manage with your distro's package manager instead of cargo?
Today Firefox have all the rust deps bundled (similar to cargo bundle). If / when tomorrow the maintainer of the distribution find a bug in one of the rust dependencies, s/he needs to add the fix inside the bundle without a clear process (1. do I need to fork and update Cargo.toml to point to my branch? 2. can I add the fix as a .patch and apply it after it gets unbundled by the build server? 3. ...)
An also this process needs to be repeated for each application that have this version of the crate as a dependency, and again without a clear way of identifying those applications that are affected.