The aesthetic sports have long put pressure on the thin ideal. It isn’t just the aesthetic sports; runners, horse jockeys - any sport where being a lighter build is perceived as an advantage. It can be up to a certain point and it’s an extremely fine balance before descent into relative energy deficiency in sport - REDS - formerly known as the female athlete’s triad, with possible short and long term negative impact on health.
That said, any athlete who trains to an elite level will likely have low body fat. A thinner, lighter build can be advantageous for doing larger jumps but you also need the muscular strength (legs, core and arms). Similar to a well conditioned dancer, light but incredibly strong and also built for endurance, similar to a long distance runner (they too tend to be built on the lighter side than sprinters). With men and pre-pubescent females, thinner/narrower hips help with the rotations. At the end of the day, a young athlete should have a good support team (coaches, family, friends) who are aware of the pitfalls of aesthetic sports and are there to encourage a strong and healthy body. Sadly, that’s not always the case - peer pressure both through sport and school, where strong legs may be said to be fat or large, or even misguided advice from parents and coaches.
The harsh reality is that if an athlete wants to have any hope at longevity, they need to be strong and healthy, eating well, resting and sleeping well to enable recovery and growth. Thankfully, especially with ease of access to information, it is a lot easier to educate yourself if it is truly your passion. There is a lot more information on RED-S, overtraining, fuelling a body to work etc.