Actually, among great mathmaticians who also won gold medals are rare, so you can use your one hand of fingers to count them. Math competition may block true math genius to come forward, those who have passion in math, but not are interested in competitive enviroment, or those who love one part of math, not number theory and claasical geometry,
Many things learned in math competition has no use in true math research, even it may help them to get A in classes. This could be reason that many gold medalists have difficulty to transform them into reality that there are questions they can not solve.
Math research is a combination of hard work, intelligence and luck.