Actually, they've provided evidence (somewhat flawed) that you've tried to wave away with other evidence/preferring another rate (that seems more flawed to me).
Religious organizations have a) smaller number of personnel, b) fewer youth contacts in total, c) lower hours of contact per average youth than your comparison organizations. We can debate about the importance of each of these in the denominator, but they're all signifiers.
Worse, you're trying to compare numbers for schools that include student-on-student sexual violence (the vast majority of cases) to complaints against staff and clergy for churches.