I think it is pretty reasonable the way they do it. I am sure they don't even go by school, but often by class rank. Sure Maybe Harvard etc will get a look, but if someone is in the the top 15% at almost any school they might get some consideration. There is just simply no way for firms that get hundreds or thousands of applicants to sort through them all. A really presitigous school or high class ranking is the best formula they can use. Most people who graduate and pass the bar can be taught to be decent attorneys, but what do you have that makes you that much better than anyone else. One of those two things.
I get to go to a basketball analogy now. My friend is a college coach and he goes to the big AAU tournaments to scout high school players. Everyone at these tournaments is good there is not a bad player out there. There is only distinguish them really is by size so if there is a 7'0 guy out there well that gives him the edge. Being 7'0 tall is like going to Harvard in the legal world. It doesn't necessarily mean you will be great, but you will get noticed and have some potential. For the guys that are 6'1 in these tournaments the only way to get noticed is by dominating and scoring 20 points otherwise the guy is just another 6'1 guard like everyone else. Scoring 20 points in one of these tournaments is like ranking in the top 10% of your class. Nobody would notice another 6'1 guy, but if you stand out for that moment then you will get noticed. The 20 points is not necessarily maybe the team was not playing good D on him, maybe he had the game of his life etc. However, it is something and you could not possibly do an in-depth look at every 6'1 guard out there.
So my point is that these tournaments are like law school. Everyone in the tournament is a pretty good basketball player from and everyone is law school is pretty smart. However, these teams and these firms only have a few spots to fill and they are looking at thousands of players or students. You can set yourself apart in the legal field by going to a badass school or getting really good grades at a lower ranked school. In basketball you get noticed if you are really tall or you put up some solid numbers when people are watching you. It is not a perfect system, but it is the only way to scour through the sheer numbers of people.