When you use gunpowder with brushes like blend ball and blend disk you just make a square of blocks which doesn't seem like a logical opposite of what arrow does.

I suggest to change the blend brushes (when used with gunpowder) to something more like the the /b e fill. Because normally the blend brushes would remove blocks rather than place. I also thought it would be useful to have a /b e fill, but working on layers (disk) for the gunpowder on blend-disk.