It's not the type of certificate that makes the aviator. A truly proficient pilot will seek out and learn all the knowledge he (or she) needs to improve his airmanship and perform his duties safely and confidently, regardless of whether that knowledge is required by a written test or not. A truly out-to-lunch "accident waiting to happen" will conduct himself in a careless manner no matter how many exams you make him sit through during his training.
Pretty much every pilot group I've ever been involved with out there in the world is comprised of roughly 85% good people who try their best and do a good job, with abilities ranging between average and exceptional. Out of the other 15%, 5% are gifted, natural aviators who are truly inspiring to fly with, 5% are complete a$$holes, and 5% are total morons who couldn't fly their way out of a paper bag.
The PILOT makes the pilot, not the paper in his wallet.