Since there is no objective definition, anyone could be one. If you have to run a 4.3, bench 250 lbs 20 consecutive times, jump to a certain height, etc., than a large portion of the best in any sport in the world are not that. Someone with specific aptitude for certain skills is better in pretty much any sport than an A level athlete. Not many soccer or tennis elites are that, and baseball in many instances also. Since those sports give you millions per year, I am guessing the mythical A level athlete would join them and be the best if they were able to with that much money involved.