The tennis comparison is completely wrong. What you've basically said is "you can't be a mathematician unless you have an iq of 150+". Yes I know, an exaggeration. All tennis players are able bodied human beings who have the talent for tennis. Some people are genetically pre-disposed to being good at sport.
If you're an endomorph you can't be thin, if you're an ectomorph you can't have big muscles. All tennis players are basically tall mesomorphs. Why is that a problem?
Letting a man with artificial legs compete with people who have normal legs is not a level playing field, however you slice it. He should run against other people with artificial legs, then he could say that he's the fastest on artificial legs. Advantage or not, he should not be allowed to compete with fully able bodied people.