I ship stuff out (small items) as well as receive stuff somewhat regularly, and have noticed a few things...
Ever since Covid came, shipping delivery drivers are no longer required to collect signatures on residential deliveries no matter what the package says, and we probably shouldn't expect that to change any time soon. Good insurance is key (advice from a precious metals dealer). Also, delivering to a business address, or holding at a shippers office might be preferable.
When busy sales companies that do a lot of "free shipping" do their shipping, it can be a fairly large pickup, and things may get stuck in queues along the way, sometimes for days. Also, "free" ground shipping is done at the lowest possible cost, so priority wise, those items get processed after everything else by the shipping company, and then take the slowest way. This seems to me to be more pronounced at UPS and Fedex than at USPS. I think this and the "covid excuse" is why things going UPS or Fedex seem to initially take an extra day now, it's because they can.
USPS sometimes has a problem just getting the initial acceptance done. I've seen stuff I've ordered from a high volume ebayer sit for over a week at a post office "waiting to be accepted" which I think is just scan and put in the right bin. Since Covid came this issue has been much worse, but now seems to be much better than it was a year ago; I haven't had an issue with it lately.
Where I am in the San Fernando Valley (Los Angeles), I prefer USPS for speed and Fedex is my last choice due to past delivery issues. My regular UPS driver is the best though.
One thing about living on the left coast, is it seems that so may places that want to send UPS ground are on the other coast, which generally means it takes a week if everything goes well. USPS can usually get the same package here in 3 days at about the same price, depending on the size and weight of the package. Larger items like basses and (empty) racks are still best via UPS for me here.