The previous would be the main point, while the latter is a side benefit.
The question you posed is very interesting, or is it a pun, noting that the Cantonese were more easily subdued by Chinese, because they thought that "Chinese culture was better" (as the sinocentrics would say)?
Since you've already read, "The Birth of Vietnam", you are aware of the attempts at sinicisation of the VietNamese. True, they were subdued at the same time, but remember the issue of the Lac Lords. As I noted in my other thread, the Xi Ou and Luo Yue alliance (Tay Au and Lac Viet alliance) wasn't a marriage of the prince and princess from both nations. In fact, the leaders may have been in power, but didn't take control like the legends in "King Arthur". Rather, the Regional Lords were in alliance with each other. In other words, the Regional Lords were the ones who elected them. So when the Luo Yue and Xi Ou felt threatened further by China, they came together on both sides, and elected a single leader.
So, the Regional Lords had more significance than was described in the book. They had the power to vote for a leader, but what bounded these
Lords together? Common interests for either political, business, or whatever reasons. Now, we'll also have to take into account the number of Chinese that intermingled with the tribes. Nan-Yue was kind of a "Devil's Island" to the officials, but loved by the many criminals that were sent there, because they could ally themselves with the aborigines against the Chinese, but they still would've gave the proto-Cantonese Lords more exposure to the Chinese culture and hence a tendency to defect to Chinese culture and way of life, for greedy/selfish purposes.
Also, as noted in the book, the VietNamese were harder to assimilate, because the proto-Cantonese (who put up a fight) and other tribes north of modern-day VietNam, acted as a buffer.