cl12pv2s - your assertion seems correct but only if you assume the CL line is constant and linear - if a change from 4 -2 degrees pitch on the advancing side produces the same change in CL as a change from 12-10 degrees pitch on the retreating side does, then your ratio does stay the same. Does this actually happen - without having the CL curve for the aerofoil section it is difficult to say but I expect Nick has some general principles to apply.
However, I am with you completely on the tail angle being a symptom and not a cause. Nick is implying that ETPS and many other good textbooks are wrong about the raising and lowering of the lever causing pitch up and down.