I think grading people to a standard is very difficult.
At the last place I worked I was managing people and we were given a set of "standards" to rate employees on, used to determine raises, promotions, and so on. I tried my best fairly evaluate my reports, but obviously the standards are inherently imprecise and so the evaluations are mostly qualitative. I found that other managers, wanting to do well by their reports, more leniently interpreted the standards and their reports were promoted more and treated better than my own.
So, wanting to do well by my reports, I re-calibrated my own evaluations to be more lenient. The other managers responded in kind. This arms race continued until upper management found it to have essentially broken the whole system. So then we were asked to rank the performance of reports on our team. I liked everyone on my team and wanted the best for all of them, but also had no difficulty putting them in order from most productive to least productive, with maybe the occasional tie here or there.
Anyway, the whole experience kind of highlighted to me some of the issues with "objective" standards and some of the benefits of relative standards.