Nobody can possibly be this stupid or ignorant.
“Priority” mail, unlike it’s predecessor “parcel post” (on which Priority pricing was originally based) has an approximate delivery time of two days. That was and is an effort by the USPS to compete with UPS and FedEx expedited delivery.
There’s no guarantee of two days and they say that explicitly. First class can routinely take a week. The USPS makes no guarantee at all on first class.
If first class items happen to go onto the same flight or truck as Priority because there’s room to do it, that’s a good thing.
Get it? A good thing. Someone is getting expedited performance they didn’t expect.
And, no, you can’t ship first class and expect Priority delivery because some moron on an internet chat board said so.
As for the post office in general, and union hacks like you, we need to get rid of it and you entirely, it should all be done privately. It can’t happen soon enough. “Priority” notwithstanding.
I remember a couple of decades ago (late 80s or early 90s) the Post Office’s slogan was “Priority Mail 2 pounds, 2 oz, 2 days GUARANTEED”).