Working hours and conditions on the mainland are even worse than in HK, famously so.
If the office language gets pushed more towards Mandarin that doesn't help locals. The uneducated don't speak Beijing'r Mandarin just like they don't speak flawless RP English. They will still get overlooked, but now the their bosses will be princelings from the north instead... Yay?
For example, the recent National Security Law allows non-jury trials, which seems to me taken directly from the Northern Ireland playbook: https://en.wikipedia.org/wiki/Diplock_court
There are a some interesting NI court case(s?) which I've encountered in the past couple years relating to riots that were occasionally cited in the Hong Kong court which escapes me right now.
Anyway the point is that while freedoms are indeed being eroded in Hong Kong, it's a fallacy to paint the British colonial rule as benevolent just to make a point. (Most of the freedoms were granted to Hong Kong in the 1990s _after_ UK signed the Sino British joint declaration, it worked as a narrative to kind of force the Chinese government to revert a bunch of freedoms and hence the UK escaped most of the blame for making much of those those repressive laws in the first place)