I repaired those sorting machines at the Postal Processing & Distribution Center in Tulsa for 30 years, retired now. The machines which DeJoy removed were excess letter sorting machines. With first class and other letter type mail being down in volume, they no longer needed as many. When I started in 1994, we had five AFCS (Advanced Facer Canceling System) machines which ran pretty much constantly from around 4:00 until they were done around 10:00 pm longer during Christmas and on April 15th. When I retired last year, we had three machines, (newer, faster machines) which would start around 6:00 and run until they were done around 10:00, many times sooner. Often during the run, they would run out of mail and sit idle.
The big push now is toward package sorting. They are adding machines for that purpose. They run all night, finishing up around 5 or 6 in the morning, leaving a small maintenance window before firing up again in the early afternoon, sometimes sooner.
As far as why DeJoy was hired, it was to improve the service and make it self sustaining once again. We had too many PMGs who liked the status quo. He tried to shake things up, but, just as with Trump, he ran into many road blocks by Congress and others, including the unions, who didn't seem to want anything changed, even if it meant improved results!
My wife and I ship quite a few parcels out, mostly using USPS and have few complaints or late deliveries. I will also use UPS or FedEx if the price is right. I do not however use DHL, they are the slowest it seems!