Keep in mind the topic is "how is China able to provide enough food for 1.4 billion people", which implies they must have some efficient or cheap way. And I'd agree "rice" probably is one of the reason.
However, you firstly used "Shanghai's white-collar" as an example, which is the least representative group for this topic (because how cheap the food is is less of a concern for the high-income groups).
You also mentioned obesity, which only dramatically increases when China got richer. Again, totally irrelevant to the topic. If anything, Chinese people probably eat less rice now due to the increase of variety.
I do not thing that being a dietician gives you much authority to comment on the cross-cultural socioeconomics of nutrition, sorry.
The claim that the Chinese are fat and unhealthy because they are force-fed empty calories remains unproven.