Why give him credit for Estrada and Sanchez? Estrada isn't magically using a sinker most of the time, like the others, and has credited Navarro for his new pitching approach last season and Martin this season, not Walker. Sanchez also came into camp throwing CH and 4SM and is stuff is so erratic that it's difficult to predict the location of 2SM.
Pete Walker has been quoted numerous times for his love for "pitching to contact" and 2SM, so it's a logical conclusion to draw.
And for the record, I don't think it's dumb to blame hitting coaches. If they added no value to the hitting, there wouldn't be jobs for them.