You are correct, but the planned extension of the CTA Red Line includes a new station that is shared with the South Shore, creating a brand-new connection ability that never existed before. The planning for the new Union Station to McCormick Place link involves connecting the CTA, Metra and South Shore lines.

If you are standing in downtown Chicago, you can jump onto a train and conveniently go to O'Hare International (Blue Line CTA), Midway International (Orange Line CTA), Milwaukee International (Amtrak), and South Bend Regional (South Shore). South Bend has daily non-stops to NYC so I'm not sure why it's called a regional airport, but, well, there you go.