@Ana1234 - I think it pays to bear in mind that it's very difficult to quantify how nutritious a particular vegetable might be for particular people. Kale, for example, is currently being touted as the best green vegetable for nutrition by a lot of people, and it does have a lot of really good nutrients like iron that might not be common in other kinds of vegetables, but that doesn't mean you should try to survive on just kale.
No matter how nutritious individual kinds of cabbage or other vegetables might be, a varied diet is always going to be better for you because it will provide a wide range of nutrients rather than a lot of a select few.
So Chinese cabbage probably is a fantastic addition to a diet but it shouldn't be the case that people "switch to it" and abandon eating other kinds of cabbage altogether. Red cabbage in particular has nutrients that aren't available in many other places.