To give you some idea of how much MLB benefited from the multi-network approach in the late 70s and 80s, in 1978 NBC actually dumped several NFL games from their schedule so a World Series game could air on Sunday afternoon. CBS even had Pete Rose in the NFL Today studio to forecast the World Series. And in 1986, when a rainout pushed Game 7 of the 1986 World Series to Monday Night opposite Giants-Redskins (two powerhouse NFL teams at the time), the World Series blew out MNF by over 5 to 1. (something like a 38 rating to 8).
The NBC Saturday afternoon Game of the Week combined with a weekly ABC primetime game was the ideal exposure. ESPN offered too much to the point of boredom with lesser announcing caliber than what NBC and ABC had provided and the real crime is that for the last 22 years the two best baseball voices in network sports, Al Michaels and Bob Costas have been shut out of the game because they've been working for the wrong networks (Costas does do a few games for MLB Network but that's very minimal involvement). If people were able to see the World Series rotate year to year among Michaels-Costas-Buck then people wouldn't have gotten so sick of Buck as they largely are now.