Where are you wrong? You believe the USPS.
I ship about 4,000 packages all over the country every year, split about evenly between Priority and 1st Class, all with Delivery Confirmation so I know exactly when they arrive.
Actual average Priority delivery time is about 2 days, rarely does a package take 3 days.
Almost never does a 1st Class item get delivered in 2 days, the average is about 4 days, a week isn’t at all uncommon.
That’s reality over a large sample size and has been for years, regardless of any BS boilerplate on the USPS site.
Priority is dependably fast. 2 days coast to coast. Mail it Saturday and it’s there Monday. But it’s expensive for over one pound. I’m always amused at how I can ship a two pound package to anywhere in Canada for less than it costs to send that same package from San Francisco to Phoenix. That’s because the weight limit for international First Class is 4 lb., as opposed to 13 oz for domestic.
Sorry, I meant to say a one pound 8 oz package.