Is this really a problem? Every package/dependency manager seems to blow up on occasion. Gems haven't given me the problems that I've had with Pip/CPAN/Autoconf.
Well, bundler solves a problem that's related, but tangential to what rubygems does. Rubygems is first and foremost a packaging format for libraries. It handles loading, provides a common format to specify dependencies (gemspec) and a default code layout for libs. It does not to dependency resolving.
So what people used to call "gem hell" was actually "I need to specify all my dependencies and take care of conflicts myself." That's what bundler does. And it uses rubygems to actually retrieve, install and load the gems.
The only Gem hell I know of is when using distro packaged gems. They tend to do weird crap like changing dependencies or backport fixes instead of packaging the new version.
There are things more funny to do than solve bugs introduced by a backported patch.