I am not a Rust expert but the thing with the standard libraries is that it only has peer dependencies with itself and they are all synced to the same version.

Meaning if you only use the std lib you:

1) Will never include two different versions of the same peer dependency because of incompatible version requirements.

2) Will usually not have two dependencies relying on two different peer-dependencies that do the same thing. This can still happen for deprecated std lib features, but tends to be a much lesser issue.

These two issues are usually the ones that cause dependency size explosion in projects.