From a cars-on-the-road and fuel expenditure perspective, the latter sounds better.
If Amazon customers ordered like Costco shoppers, the Amazon model might very well be better. But they don't, so it isn't.
These are only comparable in an academic business model comparison, in reality, these are different retailers selling different things and consumers behave differently depending on context of what they’re buying. A lot of people want low cost on food, meanwhile, they’ll spend superficially on disposable plastic junk with very little practical value. I’m taking about the American consumer specifically when I say everyone.
Go to work, take a 5 minute detour to stop by Costco for your prescriptions, gas, and groceries on the way back
One truck per delivery service
We’re usually to “blame”. We don’t do coordinated orders in our household. We have 3 people ordering individually and I know I sometimes place multiple orders per day. But, I’d expect that shouldn’t matter and they’d notice all these orders with the same address could be put on the same delivery truck. Instead, it seems they just process orders as first in first out.
They have recently added a feature in the delivery options if I already have a pending delivery it will say “add to your Tuesday delivery” or similar, which I’m likely to choose. For a while they really wanted me to use an “Amazon day”, which would be like picking Tuesday as the day of the week my deliveries would come on. I specifically pay for Prime to have fast delivery so I don’t understand why they ever thought I’d go for that.