Maybe-- but that's a tough conclusion. While the USPS is a government agency, we still don't have enough data about the agency, or any agency's efficiency to be an accurate judge. It'd be great, for instance, if we could see what the average price per employee at the USPS was vs. UPS vs. FedEx. Sick leave comparisons, purchasing efficiencies, etc.
Lots of this data isn't available though (which is why I have my job)