I'm not sure that I understand your question. The editor's paint tool is just as important for world maps as it is for normal scenes. It's crucial for painting detailed normals on your terrain to bring it to life. It's also the optimal means of adding flora (in paint layers) while maximising player fps. It's just too crude to provide diffuse colours. The paint tool paints in crude mesh triangles. Normal scenes are on a different scale, allowing blending and carpets of flora to paper over its cracks. On a world map, performance won't allow as much flora - no breeze driven grass to hide crude and repetitive textures. World maps rely on 16,384 x 16,384 vista textures for ground colour. Even at this high resolution, we're only getting 1k resolution per node in a 16 x 16 map. So, the vista needs paint layers that add detailed normals to the vista normal and area or splatting textures to the diffuse vista.
Unfortunately, at the moment the game engine is heavily locked on tilesets. A custom world map at the moment will have washed out colours in game and only the first layer's normals are blended with the vista normal. Hopefully, TW with respond to bug reports posted on this problem and correct this and other campaign map issues.
Post in thread 'Custom main maps have had severe issues for several updates now'
