Everything you said was true except the freshest fish still comes from distributors local to the area and then sent by air. And not frozen.

Your huge Midwest guy probably is trucking it in with full reefers at a lower cost since he does volume. Since the trip is long and over very hot climates with reefers are coldest at the front I'd bet it's frozen before shipment. (I once unloaded a reefer full of eggs that only went 300 miles and there was a huge difference in temps from rear to front)

The large grocers are also trucking stuff, most likely frozen as it also has to go through links in their distribution network.

That doesn't compare to fresh fish packed in ice shipped via air.