In the US and the UK (where the interviews were conducted) Amazon deliveries are mostly contracted out to Delivery Service Partners who are small businesses that work exclusively for Amazon, drive Amazon vans, and wear Amazon uniforms. Amazon puts a lot of pressure on DSPs while giving DSPs the digital tools to apply pressure to their drivers, but there isn't a fully direct link and you can expect variation DSP-to-DSP and day-to-day.
Also, trying to calculate something as complicated as delivery routes to the maximum a human can do is bound to have outliers on either side. Eventually Amazon will figure it out and fix it, or they won't because the driver is smart enough to intentionally slow-roll it and feed them route data that validates their prediction.
https://www.protocol.com/workplace/amazon-delivery-program-t...