The thing you're missing here is the privileged place "/usr/bin" has on the filesystem. It is reasonable and proper for a package to expect to install a real, unadulterated version of itself in the standard user path. You can't simply say "well, developers can just install their own version" while at the same time installing a broken version of Ruby in the standard path.
The right call would have been not to package Ruby at all.
I think it may even be true that distribution maintainers should look at installing the scripting languages their OS requires in different privileged places and version-locking their system scripts, as upgrading Python from 2.4 to 2.7 can break some system scripts, yet useful tools like Mercurial don't like very old versions of Python.
The right call would have been not to package Ruby at all.