That, in itself, lowers performance qualifications. Would this hypothetical "she" carry less gear into a building in an emergency, or would a victim suddenly weigh proportionately less if a female firefighter is charged with the rescue?
If a women and a man each qualify to be a firefighter under the same standards, are they both quailified to have the job?
IOW, if an applicant had to lift 150 pounds and carry it 50 yards, and demonstrated he or she could do it, what difference would it be if it were a 5'5" woman or 5'5" man?