Unfortunately I can not post images yet. Here you can see hashrate distribution among pools https://www.blockchain.com/charts/pools . As far as I know (not sure) most pools are Chinese. So China already control most hashrate. And as for me it is a little bit scary 
But there are also a lot of mining farms outside of China, and we don't know what is on the government's mind, they have been thinking of banning bitcoin mining already, and that's why those big miners farms in China has a plan B already. So I would agree with your concern, but so far there is no incentive either from the government or the Chinese miners itself to sabotage bitcoin so I think we are safe by now. So that is the safe guard we have right now, Bitmain and other mining pools gains nothing about bitcoin centralisation or even a 51% attack.