I can say for certainty that Amazon delivers to my block every day. Adding 1 extra package is definitely more energy saving than me driving to Costco for the same thing.
In the city, I used to see multiple Amazon delivery trucks per day. On the rural road I now live on (dead end road with fewer than 30 households), USPS does most of the Amazon delivery, but this is somehow enough people that we see FedEx and/or UPS drive by pretty much every day in addition to USPS obviously driving by six days a week.
Given that they're also visiting the neighboring roads, it's definitely enough for an economy of scale.