i have the 16-70mm F4 and leica tri-elmar 28-35-50 mk1 (for A6000 and A7r) my results are not as bad as theirs..... in fact i think 16-70 beats my leica in certain light conditions....
i also have contax N 24-85mm...much better than 24-70 FE and 28-70 FE.....