Literally no one is asking whether China is relevant to Europe
China is not relevant to the entire rest of the map which is what people are saying
Trade routes do not need China because China would have little to no interaction with the rest of the map regardless of the silk road or not
Quite a few people are saying that China isn't relevant to Europe. Not you specifically, but other people are saying that because China's not relevant to the Crusades or Medieval Kings then it shouldn't be in the game. Now, there's a simple answer to the "It's called Crusader Kings/Europa Universalis/Victoria" argument, which is the potm-nominee one about Hearts of Iron not being about robot surgery, but that's been posted so many times already.
That said, China was relevant to the rest of the map, directly or indirectly. The Silk road for instance. Having the Silk Road kingdoms on the map without China is a bit like having the Mediterranean on the map without north Africa. The Tang Dynasty directly interacted with the states to the west of it and those interactions often took the form of armed conflict. True, the Tang collapse not long into the CK2 timeline. But they are followed by the Uyghur Khaganate, a central Asian power which is basically impossible to correctly represent without China. And they co-exist with the Tibetan Empire, another central Asian Empire that doesn't work without China. The Kyrgyz (who are already on-map, although slightly misplaced) destroy the Uighurs, creating a power vacuum that is filled by the Kara-Khanids, the Liao or Khitan empire, and finally the Kara-Khitai. All of which interacted with each other, with the much-reduced Chinese civilisation to the south, and with the rest of the CK2 map.
What I'm trying to say is that CK2 can't properly represent Europe without the middle east. CK2 can't properly represent the middle east without the steppes. And CK2 can't properly represent the steppes without China.
What are the options? A) spend a load of time, money and effort making a poor attempt at China (which most players won't play in) and force loads of people to upgrade their systems in the process. And B), leave the steppes as they are, divided in half with some of the most important parts missing. Not many players play in the steppes because the game mechanics don't quite work there and because of all the big, boring provinces. Not sure what a loss there would be from not including China.