You are comparing the current state of the Blue Line against a proposed system, though. The argument is that you could improve the Blue Line significantly for $1B, and also that there's good reason to believe it's not actually $1B.
(Doesn't have to be the Blue Line! Metra at Jeff Park or whatever with a track to OHare makes a ton of sense too.)
If we were going spend a cool billion to improve the Blue Line, I'd spend it on anything but making the airport experience better. Make the stations ADA-compliant. Use the extra space on the Congress branch for triple- or quadruple- tracking. Upgrade the power system.
But again, this is $1B not coming out of the CTA budget, it's $1B Elon Musk has burning a hole in his pocket.
(Doesn't have to be the Blue Line! Metra at Jeff Park or whatever with a track to OHare makes a ton of sense too.)