While you are correct on some of that, that is some good revisionist history. The Sox finished first or second in the division 20 times in the past 50 years and 16 in the past 30 . While that means to 70s and 80s were very lean, it's hardly what I would call rare. In those years they were in the race for most of the season. Those were meaningful games.
The Cubs on the other hand finished first or second only 13 times in that same time frame. They've only very recently been better. In the past 30 years its been 8 for the Cubs compared to 16 for the Sox.
The comparitive records and team quality hasn't been the issue. It's been the Cubs on WGN and the Sox stupid idea to try sportsvision in the early 80s, which was bad idea at the time but all teams are doing now.