Bob -- nice write-up and pov. I haven't examined Perfect Layers, but I can certainly vouch for everything you report (not that my added voice is needed). I'm not sure how and to what degree of subtlety masks are created in PL, but in Aperture, using the strength slider of the brush (not the overall Brick slider) and the feather tool one can create quite usefully ramped transitions across any mask edge and within the mask itself. The various "mask" overlays make the mask easy to see and modify. The additional ability to separately brush in darks, lights, and mid-tones gives the user a degree of control that in my experience is adequate to any task.
I assume you know all this. I wanted to add it for any who might come this way looking for a comparison of PL and Aperture. I think the extensive control of Brush masks and the interaction of Bricks is one of the least appreciated of Apertures many strengths.