I think the biggest takeaway here is that walk rate doesn’t matter very much at the lower levels of the minors. In fact, it’s not predictive at all for players in rookie ball or Low-A. And even as high as Double-A, a one percent change in strikeout rate affects a player’s projection by about 1.5 times as much as a one percent change in walk rate.
Intuitively, this makes sense. A hitter doesn’t need to be particularly good at hitting to run a high walk rate in the low minors, as pitchers at these levels often have little idea where the ball’s going. As a result, batters can get away with taking an ultra-passive approach in the hopes they’ll see four balls before they see three strikes. That strategy might work in Rookie ball or A-ball, but it can lose its effectiveness in the upper levels, where pitchers have a better handle on their control.
To be clear, this isn’t to say that a high-walk prospect is no more likely to make it than a low-walk prospect. Walk rate generally correlates with future success, but only because it’s collinear with ISO. Simply put, players who hit for power also tend to walk a lot, but it’s the power–rather than the walks–that predicts big league performance.