Rust has the deadly combo of static linking, dependency unification and a feature flag system. That makes it hard to share cached dependencies between projects,

Rust has the deadly combo of static linking, dependency unification and a feature flag system. That makes it hard to share cached dependencies between projects, and when your compiler is as complex as rustc the individual files will end up big. It's definitely possible to optimize the rlib format, like representing generic types as a tree of short IDs instead of a string or separating them into an optional debug file. Or do it like Zig with a new IR designed to be compact and easy to assemble into final executables. Even a simple global cache for the times you get lucky and end up with the same hash could help. The problem is no one on the core team has time to do it because they are always overworked from the amount of bugs that need fixing. They also have a culture of making sure all changes are perfect before they go stable as a overreaction to C++ shipping half baked proposals. I think these are the reasons everything is moving so slow.