BlueSkies, You make the case for not using labels--and not to cling to a label as something written in stone. I don't think your premise can be argued with--not by those who honor the capacity of human potential.
In this case, I see it as looking at a constellation of behaviors which have existed as primary features of a persons personality over several decades and PREDICTING that it is highly probable that these behaviors will continue. It is the observation of many people, over time, that says that persons with arrogant posturing and little demonstrated capacity for genuine empathy are exquisitely sensitive to criticism and notoriously resistant to any form of therapy---when they are willing, it is usually a manipulation to improve their image or position with another person--not for the motivation of self-improvement.
In other words it is a prediction based on tons and tons of evidence. A partner of such a person is generally advised of the reality of this preponderance of evidence---in order to make decisions for their OWN life. It seems humane to advise that to hitch one's wagon to this star, would, in all liklihood, be to face a lifetime living off the thin gruel of empty hope.
It is not just a question of "can a person change", so much as: "what is the liklihood that he will want to change". Sometimes, that liklihood is very close to zero.
A label is a word symbol used to communicate an image. Handy as a shorthand for professionals to communicate. I agree that labels should be avoided whenever possible.
sincerely, dandylion