Think there has to be some sort of separation for modern era. It's kind of easier to have skyhigh TV ratings when that's the only real medium for consumption, I think.
The highest rated and most watched NBA Final series was 1998 NBA Finals between the Chicago Bulls and Utah Jazz,; the series averaged an 18.7 rating / 33 share and 29.04 million viewers on NBC. The lowest rated and least watched NBA Final series was 2007 NBA Finals between the San Antonio Spurs and Cleveland Cavaliers; the series averaged a 6.2 rating / 11 share and 9.29 million viewers on ABC.
The 1987 NBA Finals between the Los Angeles Lakers and Boston Celtics was the highest rated and most watched NBA Final series on CBS averaging a 15.9 rating / 35 share and 24.12 million viewers. Game 7