Having the top of the strike zone at the shoulders as it was when Sandy Koufax was pitching because the shoulders are a clear demarcation, is much better than the current half way between shoulders and belt (top of pants). But that makes the strike zone pretty big as the bottom is the knees, even if it's top of the knees.
In thinking about that I wondered for the first time about why the strike zone was ever below the belt. Try taking practice swings. Do you ever swing below the belt? Our arms are attached to our shoulders so having the shoulders define the strike zone makes sense. But why the knees?
If you were going to eliminate one, why eliminate the shoulders and not the knees? The current strike zone is basically belt to knees. If you were going to cut it in half, why not use the top half, which is also closer to the eyes?