'defining fitness' is difficult to say the very least. running a race can't judge if one person is more fit than another; the word fitness is VERY general- it covers all kinds of things from endurance to strength but even more importantly (this is arguable) general health! think of it this way: if you have a person who has poor lung capacity (like me) or can't run for some other reason- and they run a race against someone who can run, but might have horrible cholesterol, be overweight, or be unhealthy in some other way- that person might win, but it doesnt mean he's in better shape. (it's a bad comparison, i know, but it works)

i can almost promise you that almost every person you ask for their definition of fitness will give you a different answer.
but i would guess that they will ALL tell you that the outcome of a race will NOT tell you who is the more physically fit of the two.