There could be something to that. I have only had a chance to measure the 800 D3. But that is a much more expensive speaker.
The blue trace is on axis, the black 90 degrees off axis.
The roll off above 15 KHz is from omni mic.
Here is the another way of looking at it. You can see though even in the 800 D3 there is still excess energy around 10 KHz. I think that is audible. I'm not sold on the idea that diamond is a great material for a tweeter diaphragm. It can, and does shatter.