Without really trying to disagree with you, at some point success has to be on the individual player. They are the one in the box. They are the ones trying to determine what a pitcher is trying to do to them. They need to read the pitch and then decide to swing or not.
And in the case of Sano, with the amount of pitches he didn't make contact with INSIDE the zone, there's something else going on there that's likely beyond coaching and engrained in his approach and/or ability.
And then there's also the fact that some players will respond better or worse to a given coach's message.
Personally, I think the overall brutality of the offensive output is a much larger indicator of coaching than any individual performance does.