You are looking at the aftermath. Also, you could have manually put `strip = "debuginfo"` to avoid the 4 MB binary even before that; the issue is about the default when no `strip` option was given.
Indeed we could always strip the binaries and I've done so on every Rust project I worked on.
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.
Oh well.