Maybe for 'gym rat' climbers. Gyms have larger holds and steeper walls. Climbing in the real world is more about balance and legs/feet. You almost never hang off your hands. Instead you are gripping tiny flakes of rock in an effort to keep weight over your feet. Hands and fingers will get abused in cracks (something gyms dont have) but im not so sure about grip.
Yeah, I think people are also confusing grip endurance with grip strength. Pulling a 500+ lb bar off the ground requires more grip strength than climbing on the walls supporting your body weight.
Also, different parts of the finger. Outdoor climbers use tip, indoor climber the first two knuckles. Weightlifter use the whole hand, which is probably best for measured grip.
