You might have had the small grains concaves and rotorcage in it, which is no good! Agreed, with that setup they are hopeless!
But with the rice outfit, they are unstoppable! I have seen those those things absolutely slaughter STS's in wheat! Nothing wrong with the samples. You just gotta back your concave off, and let the rotors do the work, and then just drive them like you hate them.
If you go exotic with them and open the forward part of the concaves under the rotors an inch, so you can shove more stuff into them they are like mad howling beasts in a wheat field. If you get the error code for fuel return temperature to high, you are doing it right. I know for a fact its the same story in milo, and most leghumes.
In corn i would agree there could be some issues, and i agree to the fullest they are useless in canola full stop. In an overall perspective the STS is more versatile, but that has its drawbacks as well.