My Superwinch has a similar mounting, simple washer and square nut captured in each of the slots on your photo Shayne. IMO, the mounting system doesn't have to be very substantial. Pull on the winch holds the feet of the winch in compression against the mounting face of the tray or bumper, so all the bolts do is prevent sideways movement, and the winch falling off when not in use.
On this theme, the mounting feet are in weak cast material, for the same reason, IMO.