You just explained UPS to a "T"
It's certainly a similar dynamic compared to the other three, although I think our situation differs in that a substantial portion of the UPS drivers actually do care about serving the customer and still can succeed at doing so a majority of the time without the near constant interference and ineptitude from the boardroom. (FedEx also still has some well trained drivers in its ranks as well)
The one big advantage Amazon holds over the other three with regard to strategic planning is that it has the most up to the minute real time data on what the customer is buying so in theory they could be in a better position to proactively allocate resources more efficiently compared to UPS having to react and pay for unused capacity in areas they were caught short in during the previous peak cycle (Rental trucks taking up space for instance).
Can they turn that leverage into a long term advantage that renders UPS obsolete? I'm nowhere near convinced of that. Most every UPS driver has seen the just how much commitment a new hire at 17 or 18 dollars an hour is willing to show and that's with the understanding of gradually achieving an hourly rate of around double that. How many Amazon employees are going to feel like lifting 150 pound parcels for nowhere near that potential hourly rate while billionaire Jef Bezos demands concessions in other areas any time those employees even ask for a raise? None of us do this job for the scenery or the working conditions. We do it because we feel at least to this point in time we are at least fairly compensated in exchange for dealing with often very poor working conditions.
I can remember a time around 15 years ago when folks were here predicting the beginning of the end when the German Post Office managed to do an end around with the acquisition of DHL and how we'd all be on the street within a couple years. It didn't take long to see how that turned out when they purged any delivery talent that made above minimum wage in favor of "temporary" or "high turnover" personnel. Once all the "temporary" DHL employees walked out on the company in several areas a day before Christmas Eve one year, that was pretty much the end of that.
It could easily happen again on a far bigger scale.