Bill Tindall
"Diamonds are an amazing abrasive, they'll cut anything". ...As a practical matter this is true.

"The trade-off is that they're slow cutting because of their shape"...This is not true. Because they are hard the particles maintain their sharp cutting edges.

"and they're so hard they're brittle".....There is a common misconception that hardness and toughness are different words for the same property, or that these properties always correlate........ Hardness is the ability to penetrate, or be penetrated. Think how Rockwell hardness is tested. Think what the testing point is made from-diamond. Diamond is one of the toughest materials known to man. It will survive boggling crushing forces. In fact diamond anvils are what are used to generate astronomical crushing forces in physics experiments.

Brittle is a description of toughness. Toughness describes a material's ability to resist fracture.

--kind of like tool steel, too hard isn't necessarily a good thing......As an illustration of how hardness and toughness do not correlate a bar of CPM 3V heat treated to a RC of 60 can be bent to 30 degrees and then straightened without fracture.....because, while it is hard, it is also tough.

"Mounted diamonds have an additional problem. The matrix they're mounted in, whether resin or nickel doesn't stand up to the stringy swarf generated when working ferrous metals"......I have no idea what this means. Use water with a bit of detergent for lubing the stones, or better water based cutting fluid from the machine shop. There are at least two companies selling lots of this kind of product designed to abrade ferrous metals. Each has been in business for many years, presumably as a result of satisfied customers.

mounted diamond stones wear quickly......Not in my hands. My fine diamond plate is going on 6 years of age and I see no decrease in its performance. It is the material I used between wheel grinding and 1 micron final edge refinement so it is the "stone" that gets the most use in my sharpening procedure.

I see an ever increasing number of professionals employing diamonds in their sharpening methods- Will Neptune(furniture) and May May(carver) for example.

Maybe this abrasive has no useful role in your situation. But I can assure anyone willing to try diamond charged plates to support their sharpening needs for making furniture that they are a cheap and convenient means to abrade the steel used for woodworking tools. My opinion is supported by the recommendation of several abrasive companies when I asked what was the best abrasive for working tool steels.