It's not that slow?

Cargo only recompiles the crates that you edit, after the first build of the dependent crates it's quick to iterate.

Compilation is not the bottleneck, it's the human (me) in the loop that's doing the thinking and typing.

The productivity boost comes from Rust's strong type system and ownership (much better than MyPy) which practically ensures that if it compiles, it will work. There's a lot less troubleshooting/debugging of my Rust "scripts" than when I wrote Python.