Sentinel, my oldest son has Klinefelter's Syndrome. He is a 20 y.o. Eagle Scout and can't do one pullup, and very few pushups. Is he physically fit? Yes, he can run far and fast, plays a lot of ultimate, hikes with the Troop every month and competed in wrestling and baseball for years. He has endurance to spare and a resting HR of about 60. But he has very little strength for his size (6'3") because of his disorder. I can't imagine how he would have reacted had his Scoutmasters demanded a full pullup before advacing. Our Troop allows them to show improvement by going from 0 to 1/2 or 1/2 to full.
Pullups are a test of raw strength related to body weight, not fitness.