I find the logic behind the principle itself buggy as it assumes that people will not improve in what they do. Even if one gets promoted close to his or her level of incompetence, it doesn’t mean that he can’t become more knowledgeable while making experience. That by the way is almost always the case, unless you reach your hard limit (eg QI or something), then you should not get further promoted (in theory). That reality is different and the system is somewhat “rigged”, that’s completely a different pair of sleeves.