The choice can't possibly be "always between two or three competent". Less competent exist, and they have to pop up somewhere. With quotas, once most competent

The choice can't possibly be "always between two or three competent". Less competent exist, and they have to pop up somewhere. With quotas, once most competent from the lesser set get taken, only less competent will remain available. It's a trivial mental exercise, not something that requires gathering evidence to figure it out.