If I wait less than 30 mins in line at the Post Office it's a good day. The clerks are never in a hurry, plodding along with zero sense of urgency. Yak Yak Yak with the customer... yeah it's nice to be friendly and chat a bit, but do the shipping while chatting at least! The 40 people waiting in line don't give a damn about how the kids are doing, how the arthritis is acting up, etc.
The big thing that slows down the works is USPS doesn't deliver packages if it doesn't fit in the mailbox. You get a slip instead and have to go pick it up at the post office. I'd guess that easily 60% of the customers in line are waiting to get a package versus shipping something.
It's bullcrap being the postage is paid to deliver from point A to point B, not A to almost B!
Here USPS is pretty much the only choice for reasonable price shipping. UPS and Fedex are quite expensive, at times 3-4x more than USPS.