Can you conclude a result?
Resizing was applied to all these images in different degrees so as to maintain the same contents in all the images. Is this really unfair for the comparison? Can it be concluded that 135mm is sharper than 100mm? 100mm is sharper than 70mm? 70mm is sharper than 50mm? 50mm is sharper than 35mm? 35mm is sharper than 24mm? Remember that when I am talking about sharpness, I am referring to the per-pixel resolution.
What is your conclusion?
In fact, I don't quite agree with the assumption that "the longer the focal length, the better the sharpness". From all the crops, you may notice that the sharpest image appear to be the shot taken at 50mm. I would rank the sharpness as follows:
50mm > 70mm > 100mm > 135mm > 35mm > 24mm.
Although it appears that there is different sharpness over different focal length, the quantitative analysis is not linear, i.e., it is not in the sequence of 135mm > 100mm> 70mm > 50mm > 35mm > 24mm. It is obvious that the sharpest image offered by a zoom lens should be somewhere at the middle range of the focal length.
I agree that a lens with longer focal length may have higher resolution, but it is largely depends on the optics and design of the lens.