The "magic" of precision stones is not just that they are flat. Each individual grain of the stone is also flat, and in the same plane as all the other flat grains. This ends up with a huge amount of flat and parallel plateaus with sharp corners and a large combined surface area, which cut anything sticking up above the work surface. When the high spots are cut down to a flat plane, the precision stone skates on the surface like it is ice, without abrasion. It only takes a couple uses rubbing a precision flat stone on a surface that you think is 'perfectly' flat to "feel" what they do and how. It is not abrasion, it is accurate, parallel cutting of burs and other imperfections. No matter how flat an ordinary sharpening stone is, it has a bunch of sharp points with a relatively small combined surface contact area, which individually gouge out small grooves in the work.