Imagine taking a 15lbs of pennies and grinding them up into a course pile of grain-like media. Throw them into a ten inch wide bucket. Now put a hole in the bottom of the buck and place a garden hose and put about 4 gpm through the media. There is no chance that you are going to lift the heavy media to adequately backwash it. Water WILL go through it in a geyser-like fashion but only in isolated sections. After doing that a hundred times or more, water will still channel through the same locations but the rest of the media will start to bond together and solidify. Eventually, it will become rock hard and even turning the softener tank upside down will not be able to clear it out to replace it.
The sections of the KDF that does not lift during backwash will still struggle to remove sulfur until it is overloaded (READ: even heavier with flow-restricting tendencies) and compounds the problem.
If you set the backwash rate adequate to lift the media (12-14 gpm) then the light weight of the fine mesh resin would cause it to just piston to the top of the tank and it would not backwash properly. One or the other will fail.
A one-system-cures-all usually fails all. KDF does have fine qualities but is often misused.