They could compete with UPS/FedEx except their incompetant .Getting an overnight letter/package from the USPS is like pissing in the wind . Even 2nd 3rd day is a crapshoot at best . UPS/FedEx can't possibly have enough aircraft to handle all their packages/letters . Its a pretty common practice to use commercial aircraft , often the same flights for airmail , so why can't the USPS do the same if they can't handle the services people pay for like next day/second day . I had a next day arrive once in 5 days lol
Before I recently retired I had done shipping and rec. for 30 years and avoided the USPS like the plague