The Rust compiler is both dog-slow and massive (both from a source and binaries perspective), and doesn't have a working incremental compilation mode yet, or support in-process hot-patching. There's no Rust REPL (hacks like papyrus don't count). Poor structural editing support. Integration with various editors/IDEs is lacking (e.g. there's no support for reporting possible performance issues with code constructs in any editor that I'm aware of, nor is there in-editor per-function disassembly or LLVM IR inspection, or borrow-checker lifetime annotation, no extract-function refactoring).

Cargo being good is necessary, but not sufficient.