I've never examined a Dawes kingpin........ It looks like the mainframe hinge clamp 'inspired' Brompton . Surely it's about the best way, as it doesn't rely on the sheer strength of the bolt to hold the hinge together like many of the cheap folders.
I don't see your point, since the Brompton hinge relies on a pin in shear. I do think the Dawes/Bromplton clamp is better structurally than the clamp used by most fold in half bikes, though slower to activate.
The majority of the clamping on the brompton hinge is done by the alloy hinge clamp which is held in place by the screw - the screw is not under a huge shear stress at all. On cheap folders the screw thread is all that's holding the hinge together and therefore takes all the force.
OK, I was comparing the other side of the hinge where the pin is. It is in shear, and it is a weak point in the system. As for the other side, I agree, the Brompton method is stronger though the bolt on alloy hinge clamp is under tension not shear.
WD40 is neither a thin oil nor lubricant