I don't think that Arca-Swiss has any problem with design or quality control. As has been pointed out, the clamp works in two stages. The instructions might be more clear, but if you are careful to use both stages of the clamp lever it works well and allows top loading of RRS plates. Here's how it works:
The initial opening of the lever is fairly obvious; move the silver button toward the end of the lever and swing the lever out until it stops in a position perpendicular to the clamp.
Then, look at the silver shaft that is exposed to view on the back side of the lever. Notice the repetitive conical shapes? Ok. With your right thumb over the exposed stepped shaft, grasp the lever between your right index finger and right thumb, place your thumbnail on one of the steps at the base of a conical shape and draw the shaft toward your palm (the distal end of the lever) then when it stops at the end of its travel, gently move the lever forward until it rests parallel to the clamp body.
The jaws of the clamp are now open enough to top load an RRS plate.