Some say it doesn't have enough body on driving rock music but I have never felt anything lacking. All the other qualities are so overwhelming
Yes, I think so, too. One of the best sounding carts ever made. The Airline Arms (all) run good with a cartridge VTF in the 2 gr area. When they have a solid cantilever and a low body weight (moved mass) it is also better. So the Zyx is a very good choice. But every sonic result is the sum of - analog - steps done right. The Zyx does not compensate anything, the sonic result is pure, clean and true in tone. Some say about their cartridges, they run well with this or that music and not so good with some different but I think, these comments are a result of mediocre playback systems where the owners need compensations to avoid loosing hairs while listening. Or they try to "tune" a "sound" in a personal "direction" without knowing anything about. The Zyx UNIverse is a complete cartridge. It has no weeks or strengths. It is one of the rare beasts which are done right.
Can it sound mediocre? Well, in those Systems I did select to listen, to, I never had such an experience. But, of course, when the connected Hardware has its own sonic "fingerprint" it can be possible that it can't show all of its abilities.