I have been looking through footage of some of the top rock climbers in the world today (male & female) and what surprised me is how most of them don't physically look that strong and some even quite petite. Considering the amount of strength needed to support your body weight while climbing, I would've expected the body type/shape to be more similar to a gymnast; yet gymnasts generally have very developed upper body muscles. I can understand being smaller/thinner helping to not have to haul as much weight, or perhaps it is more endurance fitness rather than outright strength that is more important?
The body type of proficient rock climbers does not often match what society wants you to perceive as "strong".
But, rest assured, good rock climbers have tremendously strong muscles (bilaterally) as well as incredible flexibility.
Physical height can represent an advantage as it makes it easier to reach certain holds, especially on certain routes. For most routes, however, strength and flexibility usually represent greater physical advantages.
Finally, what you can't see on the outside is often the most important: the mind. Successful rock climbing involves great mental prowess and strength. And if your route is complex, the ability to plan effectively is nothing less than essential.
There are different types of muscle fibers. Type 1 muscle fibers used for endurance sports like climbing don’t grow as big as type 2 muscle fibers that are used for short-term high power movements.
Also, muscle-to-weight ratio would be more important for climbers than in sports where absolute strength is more important. Having a low fat percentage matters for all sports where your own body weight is a highly important part of what you have to exercise force on.