If brush is same as ball i'm finding that hard to believe. For it to clean a groove would it not have to follow it exactly? What is your source for that statement?
The term "brush hone" has caused some confusion. There are several devices that could qualify as "brush hones".
The first is an abrasive filament protruding from a twisted wire; used primarily for small holes. The pressure that it can apply to the honed surface is a function of filament stiffness and length, and brush diameter. As the filaments wear and get shorter, the surface pressure is diminished, changing the surface roughness profile produced.
The second is a collection of abrasive filaments attached to an expanding rigid stone. The honing pressure can be adjusted for wear by expanding the honing mandrel. And the same honing machine and set-up can be used.
The third is made by Brush Research and is usually called a "ball" hone. It is conformable to the honing surface and cannot be used to correct bore geometry. If sized correctly (approx 10% larger than the bore), it can provide an excellent surface profile. Consisting of a ball shaped abrasive provides higher local contact pressure but is affected by wear.
Don't laugh too much, but I have a theory about honing and it is that it provides a surface which is designed to be worn away if and when needed.
That theory is exactly the opposite of modern honing technology. Properly sized and honed cylinder bores should be able to seal immediately and prevent (or at least limit) wear of both rings and bore finish. The ring should never touch the cylinder wall; it should ride on a film of oil. There are several areas of an engine that require break-in, rings are not among them.
Lets say you hone whilst stressing the block the best you can, as per previous posts there will still be some other minor distortion you can't replicate when it's up and running.
Cylinder bore distortion has been carefully studied for at least 40 years. Technical papers have been written by piston and ring and honing equipment manufacturers. The causes of bore distortion are known as are the corrective measures. But unless the engine builder can accurately measure the surface profiles and geometry, old practices will prevail.
The piston rings can then wear the bore to suit this new shape and this means the coarsness of finish is dependent on how close you are to final shape.
Not good. If a ring were to wear the bore surface to comply with a distorted bore shape, the ring would be worn or damaged, the bore surface would lose its crosshatch oil retention valleys and engine life shortened considerably. A very smooth surface does not contain oil and heat builds up very rapidly. Hot rings expand to butt ends, lack of oil causes micro welding in the ring grooves, blowby and oil consumption are increased. A rough or coarse surface is not cleanly trimmed by the action of rings. In fact, rings will most often simply fold the surface peaks into the valleys, defeating the purpose of a plateaued surface.