Well, wasn't Welsh largely applying this to sales people? If what the people do is essentially known and fully measurable then it's easy to look over a few years and say "John consistently delivers less than anyone else" and know you have the whole story. As soon as you get into software development it gets a lot hairier.

Another problem with any ranking system is that a ranking is static but actual performance is fluid. Just look at K1 results and then look at the records of the fighters. They've all fought each other and they've all lost to each other. So Hoost was better than his peers four times, but he also lost to those same people. You can say he is better in "win points", but this would never help you predict if he would win his next fight.