At their heights, a few extra issues made them difficult to hit. The angle of the ball had to be tough, and being so tall, their release point of the ball was probably a foot closer to home plate. At 100+ MPH, that’s a lot extra time and space for the batter to surrender.
I’m a guy who can barely make contact in a batting cage that throws straight 80mph. The talent of these hitters to be able to hit any pitcher let alone JR Richard, Nolan Ryan, Randy Johnson is astounding.