Note that the study with the shocking statistic is unpublished, and Rsbbi Pruzansky won’t reveal its author. There’s a wide range of schools that could be classified as Modern Orthodox. Without knowing more specific information about the schools, it’s hard to evaluate the numbers. As Sam2 points out, in many schools regarded as MO, many of the students aren’t Shomer Shabbos or Kashrus going in.
In no way am I saying there’s not a serious problem here. I’m just frustrated that there isn’t enough information on the study.