It is an argument against it because there is no way that the one level of mesh on M4 or the zero level of mesh can successfully fill in all of the brow needs for a male texture. It does better with a very plucked female eyebrow but the levels of detail just aren’t there for male textures unless you want them to look plucked, as well. I always include eyebrow textures on the eyebrow map but, in my mind, they have to be in addition to the ones on the texture map . . .
Double-layer eyebrows = extra-realistic? I won’t argue with that! But I don’t see it as a reason for PAs not to also include a no-eyebrow face-texture option (in products with hair and beard options, even just one no-eyebrow/no-hair/no-beard one would be helpful). That doesn’t prevent anyone from setting up double layered eyebrows, and it helps keep the hair color consistent.
For me, it is just because it doesn’t look good with overlay only (but I do mostly male texture sets). Plus, if you don’t have any kind of eyebrow mesh (like you do with Genesis), it looks very odd to have no brows.