Well, China of course can make Hong Kong "a city among dozens" if it tries hard, but today a citizen of Hong Kong has an average income of $46 000, while a Chinese citizen only $8 960 [1]. For comparison, in Korea an average income is $28 000 and in Japan it is $38 000. But I agree that Chinese government definitely is able to lower the income of the citizens to Chinese average within 20 years.
> The idea that rights and liberties are absolutely essential
First, they are absolutely essential for higher quality of life. You cannot measure it with just GDP per capita or income per capita. For example, Middle Asian oil-selling countries might have high income, but life is not very pleasant there, especially if you are a woman, a gay, a journalist or part of any other minority.
Also, it is more difficult to make business in authoritarian countries because of excess control over any activities which creates opportunities for corruption. For example, in China to release a mere smartphone game, the developer first has to approve the scenario and characters in the government (yes, they really have such requirements). Of course, officials have no motivation to hurry because it is you who is losing profits, not them. And you have to repeat the procedure when releasing an update.
Also, in authoritarian countries the government typically tries to gain control over any large enterprise, and after that the profits are going to nobody knows where (but the friends and relatives of officials supervising the enterpsie suddenly become successful eneterpreneurs) and the losses are compensated from the budget.
[1] https://en.wikipedia.org/wiki/List_of_countries_by_GNI_(nomi...