One key element is one must be a well-rounded team player, and not focused on oneself.
Well, this might not fit because not all sports are team sports.
they just come out so boring and vague.
Yeah, but not if you write something that is extremely cool... something that helps people think of it in a new way. What is your most important insight about "great athlete?" I guess if I think about it, my own insight would be something like... the greatest athletes are the ones with the clearest minds.
Your essay should be several paragraphs, right? Are you going to write about a person that exemplifies your ideal of a great athlete?
All you need to do is write 3 sentences about the exemplary athlete, and extend each sentence into a paragraph by adding examples and quotes. Then go back and write the intro after you have written a few body paragraphs.
It's easy! :-)