Depends on how you look at it. In 6A they are the smallest school, in 5A they are the largest. But their competition at the 5A level is more similar in enrollment than their 6A counterparts.
With regard to Cathedral. I never look at their enrollment. I look at their district, which basically encompasses a metro of 2 million. I'm not picking on them, in fact I have the upmost respect for Catholic football teams, but lets be real here. They aren't some tiny little school that beats up on their three times larger counterparts.