If you are able to hire and retain people that you pay substantially less to then their skills warrant and they were earning previously without adjusting their wages to their skill level for an extended period of time, then you are truly an amazing leader... or the worker is not as overqualified as you suggest. And if you are that good, you should be working at least one level higher at the organization you work if not running the whole company.

When the market is tight and the workers can't find jobs that fit with their skills, they can stick around for a while. And if after a while, they don't find a better job, they convince themselves that perhaps they are not overqualified. But at some level, that is sad, because one of the joys of being a manager is to help employees get ahead... and if you are underpaying them (the definition of employees being "overqualified", then that is not particularly noble.