On the other end of the spectrum, the notorious (in the Bay Area) Sunnyvale Costco actually demolished a nearby restaurant just to expand the parking lot.
In lieu of Costco, my family buys all of the big and non-perishable stuff at a giant discount supermarket that's closer to the edge of town, or at least it was until other stuff got built up around it. But we try to minimize the number of trips.
It results in fewer miles driven and more being done per mile driven. Each parking space gets more done per parking space. There's less retail worker overhead and the people that do work are paid better and have a higher quality of life.
The goal is to avoid the car-centric lifestyle, not to optimise it. Maybe that is a totally utopian idea in the us, though.
Your SUV with a Costco haul is probably driving less distance per person and carrying MORE per person while being a smaller more efficient vehicle.
Amortizing fuel per item or distance per item I'm betting the personal vehicle wins while also being better able to deliver perishable/frozen items.
(also the likes of Amazon are terrible to employees in order to make margin while Costco is the opposite)