Your missing the point: the overqualified tend to leave ASAP.
Training people does take time & money, even if shortened by talent & education. Say training time is cut by 50% by hiring the overqualified, and productivity is greater than usual; 6 months later he finds a more suitable occupation & salary, leaves on a moment’s notice (the conventional 2 weeks would cost him hundreds of $$$), you’ve got nobody doing the job now, and hiring the next warm body takes an optimistic 100% of the usual training time - now you’ve spent half-again longer training someone (50+100%), suffered extra downtime, and otherwise went thru a whole lot more hassle than if you’d hired the just-qualified in the first place.
Being overqualified implies that the person by definition is also qualified too. So what you are saying is you have a QUALIFIED person willing to work for the wages offered but you refuse to hire them. I think there is a small place in hell for people like you. Somebody who is qualified, hell YOU DEEMED THEM OVERQUALIFIED, needs work. Is willing to accept the wages and is turned down by a loser like you. How humiliating. A democrat is formed every time that happens.