Why should we think so?
IMHO no one has proved (and will never be able to prove) that Ethernet is intrinsically better than USB, although in our particular DACs we can have a preference. In the end all depends on the implementation, both formats are bit perfect.
First, the word "prove" does not apply to anything measured subjectively and of course outcome is a function of implementation. However, that does not mean that you don't start with a design that maximizes the probability the outcome will be considered preferable to most ears. The science behind jitter and grounding noise reduction which is achieved through direct ethernet-to-I2S in the DAC which ensures close physical proximity to the dac clock is compelling to me. That's all I was saying.