is there any way to fix such a non-intuitive installation procedure?
you can try it all on one line: “apt-get install ruby libzlib-ruby rdoc
irb”
it’s an apt thingy (as far as ruby is concern;)
apt maintainers holds, “you install only what you want, so say what you
want to install” 
imho, the ideal way is to compile fr source, plus you get to have the
latest stable too.
kind regards -botp