I've said for a while that I think that the "real" issue with compile times is that there's a ton of dead code getting compiled across the dependency tree. I personally blame Cargo features not being ergonomic enough, because on paper they're perfectly suited to solve this problem, but in practice the amount of boilerplate needed to use them for this is infeasible. I wrote a manifesto about this a while back: https://saghm.com/cargo-features-rust-compile-times/