Edge and Drybrush paints are quite different. Edge paints are the same consistency as layer paints (so, pretty thin and runny). Drybrush praints are quite thick and crumbly.
You can use any layer paint to drybrush, and as it happens, bright colors are popular for drybrushing (because usually you're highlighting the raised surfaces); hence, the overlap in colors. However, when using a layer paint, you want to wipe off almost all the paint with a paper towel or a piece of cardboard, so that the paint is extremely... dry. it is called drybrushing, after all
It is the dryness that prevents the paint from flowing, and instead just sticking onto the highest points.
So, the problem becomes paint efficiency. If I'm drybrushing terrain, for instance, I'll go through a pot of dawnstone in no time at all -- and most of that paint has gone to waste rather than my model. To mitigate it, I can transfer the pot onto a palette first, and then only dab a little onto the brush, then dry it out. But it's still pretty inefficient.
In contrast, the exact same (dawnstone) paint in drybrush formulation is much grittier, and nearly devoid of moisture, so the amount I waste is tiny. And because it's denser, one pot goes much, much further.
The reverse is also true: you CAN take thick, coarse drybrush paint and essentially turn it into layer paint. You do this by adding medium. But, it never quite comes out right and isn't the correct consistency. It also isn't easy to get it the same thickness every time, if you want to use it to basecoat or paint details. Really, it's not worth the trouble.
