Textual Complexity vs. Visual Simplicity

[Koen G]

My view remains that the VM painter did, at times, attempt this kind of shading/highlighting. But they did it so poorly that the end result looks messy or bizarre

You're showing great leniency here :-)
Well, we can't know for sure.

I have little doubt about it. The painter knows how to color in a surface, as in the opaque flowers. Only when there are vertical lines (like in the fabric), you get this vertical striping in the paint. See for example the flower on You are not allowed to view links. Register or Login to view. (top): this is someone experimenting with shading, but failing. For comparison, I include the flower on the verso, f15v, where the pen lines are clearer. (Maybe the same technique was attempted here in the faded yellow?)

See also You are not allowed to view links. Register or Login to view. (bottom): the petals, which were presumably even-colored in the example, are opaque. But where there is more depth, like in the grooves on the calyx and the buds, shading is attempted. Both are awful: there is absolutely no need to invent a separate "heavy" painter when everything can be explained by one bad painter attempting to match different techniques.