I think distros package rustup too. Here on Arch it is pacman -S rustup (instead of the curl | sh thing) then proceed normally.

Installing an outdated toolchain makes little sense because after this example people interested in Rust may want to do other things, and will encounter an artificial roadblock when they (or a worse, a dependency) needs a newer Rust.

I think the Rust packaged in the distros is meant to be a build-dependency of software written in Rust (for example, ripgrep), not for Rust developers.