It's hard to pitch around Sano if you have two OBP guys in front of him. While Sano is a beast, if two guys are already on the basepaths, it's unlikely the other team is going to walk Miguel very often. And you don't need a great hitter behind Sano in that situation, you just need a competent hitter. One of Kepler, Buxton, or Rosario will hopefully fill that role as the season progresses (man, Max was teeing off yesterday, a really impressive performance from him). Thus far in the season, we've seen the Twins thrive by stacking really annoying hitters in a row: Dozier, Grossman, Mauer, and Sano. And when it has worked properly, walks have massacred opposing pitchers. Time will tell whether that success has been a fluke of SSS or whether it's a strategy that can succeed over the long term.