I'm honestly baffled as to where they got that idea, most commercial vans are built around standard pallets and wallboard sheets. Mercedes Sprinter and Vito will, the Transit including the Transit Custom will, the Toyota Hiace will, it's pretty much a standard feature.
As in plasterboard sheets? I don't see why not if hand loading, plenty of vans will fit a 2400x1200 sheet (my Transporter fitted a bunch of plywood with room to spare). Loading one with a forklift is harder due to no side access long enough to fit 2400mm but that's a problem shared with tub back utes. If however your plasterboard pallet is side accessible a van with barn doors (like you'd buy if pallets were a priority) will allow you load it in fine.
Actually yes my ranger fits just fine in some of the tightest of places. Never had a problem fitting into compact car spots with no over hang. With a full size 8 foot bed no less.