It's reasonable to expect that apt's Ruby/Rubygems works with Bundler in the same sense as it's reasonable to expect that apt's Apache will set the right MIME type for a ".html" file, and not set it "application/binary" by default because some configuration file some Debian person thinks should exist isn't there.

Put more simply: if they can't package a rubygems that actually works with the rubygems ecosystem, they should not package rubygems at all.