You are making assumptions; you can't just assume that if he takes 20 less BB he will only get 2-3 hits because you have no idea what would happen which is why sabermetrics is so misleading. They take tendencies and call them facts. Being aggressive means swinging at pitches near or in the strike zone. With 2 RISP, if you see a pitch just off the plate you swing at it. Good hitters will still get hits. Look at Pujols, Guerrero, etc, they swing at anything close in these types of situations and are considered some of the best hitters in the game. Perhaps the 2nd or 3rd pitch is close enough to slap the other way and drive both those runners in. It just depends how the AB plays out but if you are patient and take the walk, you can't just assume the person behind you will knock the runners in. There are so many variables such as the pitcher, what he throws, the count, what point in the game it is, if the hitter is on a hot streak, who comes up next, how many outs there are, how the defense is playing the hitter...that is why you play the games. Not everything can be figured out on paper.