OT is not very good at showing lines when the Viewer zoom is not at 100%.
So I'd suggest adjusting your zoom level to 100% to see the real quality of what you're drawing.
You can quickly achieve that, by using the shortcut: 'n'.
Brush types inside the "Raster" tab of the Style Editor work only when drawing in levels of type "Toonz Raster" or "Raster".
Moreover, changing the brush type for a color in the palette does not affect what is already drawn using that color, but just future lines drawn after that.