All the Zu Audio speakers have a rising treble above 10khz. Some call this "detail"!!! Same problem with B&W speakers.
Zu Audio speakers are not the same, supertweeter is different, depends on the model, high pass network can be upgraded with different caps.
I have no problem with my Zu Audio Druid, my supertweeter is Radian 850 and there is my previous supertweeter on the same image. The hights are silky and very enjoyable.
Zu Soul mkII is way different from Druid
There is a huge difference in price between those two models, also huge difference in performance, so ZU speakers are different.