Re: athlete, genius and other.
First, get over the ideas that "gymnast = ne plus ultra of DEX" and "DEX and STR are mutually exclusive". Even if you can't let go of the former, some of the strongest athletes in the world (pound-for-pound) are male Olympic gymnasts, and that's exclusive of the cinematic context that is the default for Hero.
Second, understand how your game is scaled. As noted above, the absolute human max is 30 for STR, DEX, etc. while the explicitly optional characteristic maxima are actually cost breakpoints, and not maxima at all. Now, a local gaming group can house-rule all of this to be otherwise, so take any such house rules into account.
World/international class athletes will have physical characteristics in the top of the range for the campaign/setting, plus relevant skills, including one (or more, if the athletic competition is a major part of the campaign) PS covering the sport. As for a polymath, literary precedent (Doc Savage, Richard Seaton [skylark series], Batman) says that such characters have both world-class physical characteristics and mental characteristics to match, plus a plethora of skills of all kinds.