During the Great Depression, many taxi drivers drove unsafe cars. There were many accidents involving unlicensed drivers of unmaintained cabs. The medallion system was introduced to improve the safety of taxis by imposing minimum capital requirements, i.e., the cost of purchasing/renewing the medallion, and ongoing compliance requirements (insurance, vehicle maintainence, etc.).
Uber has not negated the underlying justification for the medallion system. All it has done is to take all of the risks that taxi companies normally accept and push it on to the drivers and passengers. Uber's disruptive edge is essentially its exploitation of its customers/service providers.
When your business is based around exploiting the financial naivete of others, you have to know that you will only enjoy that advantage for a limited window.