Folks should also carefully consider the less-visible costs of tossing everything into the standard library.
Sure, putting APIs in the standard library means you avoid an explicit package dependency, but if you're targeting Apple platforms you're now limited by what version of the OS you're running on because the standard library is part of the OS. Any time a new API comes out in one of those packages, it would require an OS availability check and/or upgrading to the latest OS to use the new stuff.
Whereas if you're using it as a package, as long as the new features don't require corresponding new standard library features, you can just upgrade to the new version of the package immediately without affecting your minimum deployment version.