Let's not forget the huge cost of aggressive expansions, at that time, as well. While I agree that many of the old barns were "holes in the wall", those came during massive expansion, and were what was available at the time.
I guess a lot has to do with local perspectives. My location, and many nearby, were built to AF specs, before FDX came along, and are quite nice. FedEx has built a lot more since acquisition, especially in dense population areas, having more than one per. I'm not really verywell versed in the "big picture", as far as barn construction goes. Don't know how many have been added/expanded, etc. I do know that when all things are factored in, long term financing, tax, depreciation, efficiency, etc, there is real financial benefit to build/expand as opposed to leasing of the hole in the walls.