The actual history of the Post Office and it's 19th Century competition is very interesting, the Post Office delivered a high-cost limited service, useful for political patronage and subsidizing politically important constituencies. Its private competitors pioneered improved methods, low-cost postage, and delivery to rural areas. It only stayed in business by enforcing its legal monopoly.
Today the USPS pays excessive salaries to members of politically powerful postal unions and fat manager salaries. It mostly delivers "junk" mail. I have no doubt that if the monopoly was lifted, we would see improved postal solutions.
Those "fat manager salaries" are less than those paid to other manaagers with comparable responsibilities.
Sure wish my salary had been "fat".