Hi Kingfish
Granted, hard stones will not so easily round a blade in part because the stone itself dishes more slower, but a faster cutting softer stone will dish to the same small degree if the same amount of actual sharpening (bevel formation) is done with fewer strokes. Here is a scheme I worked out a few years ago to compare stone hardness. I used the same blade to test each stone using the same amount of hand pressure, length of stroke and water.
So you can see by the black swarf in the water and slurry that with a faster cutting stone using fewer strokes you can remove the same or equal amount of steel. Now this is useful if you are actually sharpening a blade. If you are just polishing a blade to make it shiny then any hard stone or maybe even glass or would work.
www.thejapanblade.com/hard203.jpg