Without getting into the pros or cons of the particulars, let me say this: there are systems that rate people's skill. They're all over the place. Consider, for one instance, the world-wide rating of chess players. Their ratings are a form of the ELO system.
I could describe this in great detail, using about lebenty-zillion pages, but there wouldn't be much point.
Just let me say that win-loss ratio is meaningless. A person who wins 20% of his or her games against the world champion is clearly more advanced than the person who wins 90% of his or her games against a rotting fence post.
The implementation of such a system is sort of a chicken and egg situation. One is rated against his or her opponents, but where did the opponents get their rating?
You can find a little (very little) about this on my website. It needs a very careful formula. The formula will vary according to the ratio of skill versus chance in determining the winner of a particular game. A dice game or a card game will have more elements of chance than a game of more purely skill, such as chess. Even in a game of (supposedly) pure skill, there are elements of variation that influence the game. Maybe player A just had a car accident, or his or her mother died, while the opponent just won a million dollar lottery. The effects are real. One does the best they can to rate people honestly.