I think you’ve misunderstood...
First, I referred to a boundary layer of about ½” causing reduced conventional aileron effectiveness at about 2 degrees deflection on the wing mentioned above.
The air within the boundary layer has almost the same speed as the wing itself so its impact on the control surface is much less compared with the free stream.

Then, in the next paragraph, I added a further advantage of the “Junker’s” aileron. [8D]