Therapist – (and wouldn’t a true therapist acknowledge that there is not a one size fits all aspect to Judaism?) of course there are different standards for different people. Do we not say “chanoch lanaar al pi darko?”
A smart and intuitive rov knows that not every answer fits to every situation, even when the situation seems identical to another. That’s why the same rov can give the same person two different piskei halacha on the same shailah that occurs more than once. Or gives one p’sak to one person and the opposite p’sak to another ON THE SAME INYAN.
One girl might find it more palatable to wear a skirt that meets the absolute bare minimal requirements for tznius. She is following the halacha. Another girl might be more comfortable wearing a skirt four inches below her knees. She is following the halacha. Another might need it to be a couple of inches longer, in order to feel she is conforming to proper standards. They are EACH following the halacha. Whatever the Rov you mentioned feels personally (and he, too is personalizing our religion by making that statement), there are shivim panim L’Torah, and other halachic viewpoints that are considered valid. And that is why there cannot be a Tznius police type rabbinic enforcement, because there will never be a complete consensus in this hot-button issue. Each rov in his own Shul or Yeshivah has the authority to expect a level that conforms to his hashkafa. But as each rov has his own personal hashkafa, there cannot be, as I said, a one size fits all philosophy. As long as the minimum standard is being met (not saying that is the ideal situation), the girls are being tzniusdig. You may disagree (feel free), but thinking otherwise, is how divisiveness occurs. Right now, I am thinking achdus would be a nice thing in klal Yisroel.