Let's try and correct the record.
Staining developers are an asset for both VC and graded papers. The yellow-yellow green - orange brown stain with PMK retards blue and green light. The stain with PMK is proportional to the silver density. VC papers are sensitive to both blue and green light and graded papers are sensitive to blue light. The color of the stain retards the transmission of blue and green light and thus is effective for both types of papers.
Shadows with PMK are not muddy if the proper exposure is given to the negative. You should always test for your personal EI - however you do the testing you should aim for a zone 1 density of .1 above fb+f.
I did a test a few years ago with PMK and Pyrocat. I tested for EI and dev time for a vc paper with no filter - approx the same as a #2 filter. I then shot side by side comparisons, processed the film and made direct scans of the negatives. The PMK negative had much better high value separation. I would have been happy to change developers if the Pyrocat gave me better tonal separation up and down the scale. I did not feel it did.
If you have not read The Book of Pyro by Gordon Hutchings I would strongly recommend doing so. It is the most definitive and comprehensive work on staining develpers and how they work. You can get a copy form Bostick and Sullivan or the Photographer's Formulary. Gordon will also be doing a workshop and a presentation on staining developers at foto3.