It goes both ways, though - the tacit deal is basically that the HK tycoons do not challenge the Chinese Communist Party's monopoly on power, and the CCP doesn't challenge the HK tycoons' economic monopolies.
But, all in all, I agree. As I've written in another thread:
The grievances of HK's population are real: a political and business establishment dominated by property tycoons (and increasingly mainland Chinese political factions) keen on maintaining their privileged position; huge economic inequality; a slow erosion of political liberties ("salami tactic").
That all, of course, gave rise to the Umbrella Movement in 2014.
However, given that the Chinese Communist Party is not inclined to weaken its grip on power, and extremely protective of the (perceived) territorial integrity of China, I don't really see how this will end well. :-/ Here's hoping.
For perspective, BTW: In 1997, HK's GDP was about one sixth of China's (even though China has 200x the people), and HK was an important conduit between China and the world: HK's port had more volume than Shanghai and Shenzhen together.
Today, HK's GDP is barely 3% of China's, and the ports of Shanghai and Shenzhen together have 3x the throughput of HK. (Just have a look at these pictures: http://www.dailymail.co.uk/news/article-2478975/Shanghai-por.... )
HK used to be hugely important for China. Now, it isn't, and with rising Chinese nationalism, HK is being seen more and more like an unruly and spoiled child.