I'm with Farmer 1. Sometimes simple exam passes or failures are no measure of a candidates suitability for a role in the long term, simply a measure of their ability to pass exams at any given point in time.
I know you suggest that there are more subjective issues here relating to the opinions of trainers, but these people can be, and often are, completely wrong. I know several pilots who have had great difficulty in their initial training who have subsequently progressed in impressive fashion later in their careers, but to apply the criteria you wish to see implemented in your post would have prevented this from happening.
Sometimes an outside opinion from somebody independant to a degree from the process can be a useful addition to the process.
Why don't you tell us what your real beef is? Candidate 1 by any chance?