Defense helps pitching. They go hand in hand. A guy like Bello is going to give up a lot of ground balls. He needs guys to make plays behind him. Also, the more plays that aren’t made, the more pitches have to be thrown, which means less innings get thrown. The more pitchers you have to use on a given day, the more likely it is one of them won’t have it.
You can’t count on 6 runs a game. You should be able to count on good defense. You may not win a game on defense, but you can lose one.
Flemming wasn’t saying defense was the key to winning, he’s saying the Sox win when they play good defense. Correlation is not causation.