Sure it is, that's an inherently political argument to make.
My counterpoint: I ordered a few things from a vendor (Waytek) recently. Waytek ships via UPS exclusively. I chose UPS Ground service which would've gotten the package to me in about a week. UPS got the package to California, to the regional sorting center in California, sent me an email telling me to expect a delivery, and then got the package to Massachusetts that same evening. UPS said they'll deliver the package in another week or so (assuming they don't bounce it back to the east coast). Despite being able to ship it on their dime cross-country in less than a day, they've put the package on the slow boat back to its intended destination. The UPS response has been: keep an eye on the tracking number and take it up with the vendor if you have any issues. Waytek's stance is that it's officially my property and their duty ended when they dropped the package off with THEIR shipping vendor (UPS).
Tell me again how private corporations are inherently more accountable?
Meanwhile I've ordered replacement parts for the Waytek order from a vendor that ships USPS. The tracking information is showing an estimated delivery date of two days from now (Tuesday), but they're also showing that the package has left the local regional distribution center. That gives me about a 95% chance of having the package in my box 10 AM tomorrow morning (one day early).
There are two reasons why I called it a rant. The first was begging the question of whether that’s true, as you also made the mistake of doing, since there was no attempt to introduce data or analysis showing that the USPS is substantially worse. Since Amazon famously does that kind of analysis, cares a lot about customer satisfaction, and uses a number of carriers it seems especially unlikely that there’s some huge problem they haven’t noticed.
The second reason, however, is the error of treating the quality of government as constant and inalterable. That’s effectively arguing that there’s no difference between South Sudan and Norway, and it’s what really made me regret wasting space on a lazy rant. Even if it was true, the grownup discussion would be how we should have better management and incentives rather than assuming it can never work, just as reasonable people react to a bad experience with a company by supporting boycotts, regulation, or legal improvements rather than saying the private business model can never work.