The problem is the high stress generated by the one-shot approach. There has to be a balance between the objectivity of a single test and practical concerns (like choking because you were sick or got bad sleep the night before).

Ultimately, the only "fair" outcome is an abundance of opportunity. The vast majority of people are worth something to their community and society. And even then, as long as there's enough food and shelter to go around, no one should have to justify their mere existence.