I have been using and still use PMK for nearly all my film developing for going on 6 or 7 years and I almost always use VC paper. I found G Hutchins times would produce a slightly flat negative. I simply increased the time in the developer and viola. Really nice easy to print negs. What is the problem?
Let me first observe that Thornton was primarily a 35mm and roll film user and did not work much in large format. Therefore some of the issues he raises may or may not be relevant to your work.
First he writes that he likes PMK with graded papers but not with VC papers. There are prints in the book made from the same PMK negative, one on Ilford grade # 2 paper, the other on Ilford variable contrast , filtered to grade two. Neither print was toned or manipulated in either way. The print on VC papers clearly has less contrast than the one on graded paper. Thornton estimates the difference to be about one full paper grade.
Then he makes three points.
1. He observes that in order to get the same contrast on VC #2 paper that was obtained on the grade #2 paper it would have been necessary to lengthen time of development. But there is a downside to extending development time: grain will be more noticeable, especially in the highlight, because there will be less grain masking. This seems logical because the extra yellow density that is created by extending development time provides very little if any printing density to the green low contrast layer so the extra printing density you add to the highlights by extending development time is primarily silver density.
2. The highlights have much greater yellow/green stain than other tonal areas and for this reason are softened more than shadow areas. Again, the reason is that the yellow/grain stain does not provide any printing density for the low contrast green layer of the paper.
3. The second feature is a two-edge sword. It works well in some circumstances by allowing us to retain highlight detail in very high contrast situations, but in others situations it results in muddy highlights. And extending development time does not improve highlight separation.
Thorntons observations make perfect sense to me and they are absolutely consistent with my own observations. When I first started to print with PMK using VC papers the most immediate and obvious difference between it and other developers was the fact that it was easier to print certain high contrast scenes. However, with time I began to notice that there was a certain loss of separation in the highlights. Perhaps they were not muddy, as Thornton suggest, but they simply lacked the kind of clarity and snap I was used to. Eventually I quit printing with all silver papers and the question became somewhat mute for me, as it is now I guess.
In my opinion there is no argument but that PMK (and Rollo Pyro), both of which produce a yellow/green stain, render tonal values in the highlights and upper mid-tones differently than both non-staining developers and staining developers such as Diaxactol and Pyrocat-HD that give brown staining. Depending on the lighting conditions and contrast of the scene phographed this difference could be an advantage or disadvantage in making the final print.