You are aware that the stdlib is linked with --as-needed which tells the linker to not include unused code, right? The entire stdlib is not included in Rust binaries unless you use the entire stdlib. However, as this article shows, that does not apply to debug info.
Hrm, I read the comments of another user who contributes to Rust and it seems there is various formatting / panic / abort / symbol and location translation code that contributes to the size and currently there is not much that can be done about it.
Indeed we could always strip the binaries and I've done so on every Rust project I worked on.