[Vraxx]

While the post you're responding to doesn't explicitly state all the detail you were looking for, I do think you're being a bit too dismissive.

Not sure on the accuracy of the claims, but the "hand waving" is saying that the estimated time spent per delivery may be a large overestimate if that driver is delivering multiple orders per trip, thus reducing the amount of time that a single customer pays the driver to drive out to a specific area. Point number two was to imply that, yes, if they priced a delivery at $2 per delivery, they probably are operating at a loss, but not everybody gets 50+ deliveries in a year, thus bringing the average cost of delivery up. Heavy users have existed in other systems and they didn't become suddenly untenable (Amazon prime seems to handle it just fine).

[RodericDay]

It needs a bit more detail. Is the assumption of groceries once a week really weak? (literally everybody I know gets groceries once a week)

Is the density of drivers and customers such that drivers deliver at a rate <<15 min?

"Not everybody gets 50+ deliveries a year" can sound as sensible as "Not everybody brushes their teeth every day" or as pedantic as "Not everybody sleeps every day" depending on the underlying statistics.