I agree with you that WP:ATHLETE lets in a lot of people who wouldn't make it under general WP:N criteria, that seems to be how the specific guideline works.  It also holds true for a lot of minor-league professionals.  The general feel is that if the player can live off what they earn, it is "fully-professional."  As for the "highest level of amateur sports," then I don't know how to decide who makes the cut and who doesn't.  Medal-winning?  Final heats?  And it wouldn't distinguish between varied sports either.  An Olympic sport such as gymnastics or basketball is going to have athletes who don't win medals who are more natable than those that do in smaller sports such as shooting or curling.  you see where the discussion on levels beneath the Olympics can go.  I feel that there needs to be some bright-line rules here because of the mass of athletes involved.  In football, until this discussion, it has been interpreted to require play at the professional level without independent notability.