The competitions are a minimal sideline and are there only so young dancers are seen by the artistic directors of vocational ballet schools and professional companies. Winning a competition is not an end in itself if it doesn't lead to a job offer at the end of it. They are a stepping stone to a career.
If you are a sportsperson, you aren't having to compete whilst wearing a tutu and a tiara or dressed as a pirate, act out the character's emotions in a plot and do all of it whilst making it look effortless with a smile on your face. On stage, in front of an audience. With an orchestral accompaniment. Sometimes twice daily, to the same music and choreography, and doing it over and over again to the same exceptionally high standard. Week in, week out. Then whilst you are performing that ballet in the evening, you are also in the studio all day every day rehearsing all the choreography for for your role in whatever ballet the company is performing next.
It isn't a sport. It's a performing art.
And yes I do know quite a few professional ballet dancers.