I am sure this is true. Once a cowboy - always a cowboy. People don't change - except temporarily to make a good impression on somebody.
But the training is also lacking. Private pilot training doesn't deal with the broader "management" issues. You sit the exams, you fly the hours, and anybody who doesn't kill the instructor will eventually get a PPL. They say "a license is a license to learn, young man, now go away, I have a new customer waiting"
Short of getting clued-up by a lot of internet activity, and meeting up with other pilots (some of whom will be good and some will also be cowboys), one has little opportunity to drag oneself beyond the PPL sausage machine.
Edit: just found that article. It basically says that a study found that pilots were in two distinct groups, grouped by some fairly basic psychology. Also their ratings and total time did not make much difference to their chances of getting killed, though experience did make a difference to their chances of having minor prangs.
However I suspect that as always with these things the overall picture is hiding stuff like a higher rated pilot flying more complex mission profiles, etc.