Sure, but if some people are faster than others because they have longer legs or because they've trained more etc. then people without such advantages aren't given special accomodation. It actually runs in my family that we have very short legs in comparison to our torsos. For example I'm 6' tall but look like I'm 6' 4" or thereabouts when sitting down next to someone with more normal proportions. In spite of this disadvantage, one of my brothers did cross country in high school and still runs half-marathons every year or so. He doesn't demand to be given a head start or to have time subtracted to accommodate his inherent disadvantage, because that's the difference between equality and equity.

Following your analogy, what equity efforts turn in practice is to not only accommodate for track length for those that start behind, but also to cut one leg off of those perceived to be ahead.