You balancers don't take into account that San is really good at cav so yea he's going to have a really good score. Why San acts like the average player is going to get that score, I don't know.
If you start playing cav now all the veteran cav players are going to rape you...hard. It's a class that takes time to learn and has a much higher skill cap then infantry or archers.
No, we do. San's still human though, meaning that anything he does, even if it might seem "unrealistic," says something about the potential of what he's playing. This is true for anyone. Balancing by only considering the average, while ignoring the best players or what the actual potential of something is, would be a prime example of bias born from things like short sightedness, naivete, ignorance or more specifically, a blatant disregard of the facts. What's more though, is that even if you focus on average performance, the average cav still gets nearly twice the k:d of melee.
Don't be confused though, just because you can get more kills/fewer deaths as cav, doesn't mean we're going to nerf it. It does however, mean that classes aren't equal(at least not in some boring sense), of course we don't intend for them to be, either.