Amazon is carpooling for shopping, and the math proves it.
I think there's a bit of an error here, similar to the one in the original article, where you assume every Amazon delivery would counterfactually have been a whole separate shopping trip by the consumer that wouldn't happen otherwise.
People still go shopping. Maybe a lot of these purchases would have been picked up on a trip that happened anyway, and not added much marginal gas. Maybe they would have been picked up mid-commute or similar. Maybe without the convenience of Amazon they just wouldn't have happened.
Untangling the net effect of all this is tricky, but your math makes somewhat implausible assumptions and thus probably isn't a faithful representation of what the counterfactual actually is.
Starting with the '10 times the gas to shop yourself' and figure maybe half of that is shopping you wouldn't have done otherwise (leaving you with still 5 times as much) and then assume you'd pack all this stuff into 1/5th as many trips (rather than ordering individual items as the whim hits you) still puts Amazon as breaking even with self-shopping.
You'd have to be ordering a lot of stuff you wouldn't have made a trip for *and* be packing your shopping trips pretty efficiently before Amazon comes off as a net negative.
Maybe its not 10 times better - but I'd bet its at least 2-3 times better than shopping yourself.
Too bad he's still a smarmy assclown. And I have to admit that I dislike some of Amazon's business practices, particularly as it comes to deciding which items to manufacture their own version of based on being able to see companies which they hosts' sales data.
But I also have to admit that despite all that, I still buy shit from Amazon.
Though, on a somewhat orthogonal objection / addition to your original mathematical thesis, a fair bit of "what I buy on Amazon" is "stuff I can only possibly even *find* on Amazon".
So I'm **really** not sure how that balances out "trips I don't take because there's no point in going to a store here for *that*" versus "I'm sure *somebody* has one of these fucking things, right?" and driving to 20 stores and then ***still*** ordering it online because the answer was "Ha! Nope."
In the end, I concur with your response to the other objection, "In the end we'd just end up picking a different country" but in the end it would still be the entire carbon emissions of *some* country. I mean, "Andorra" if nothing else. ;)