Here's an interesting article citing some recent research which claims that the majority of mining power is in China, and those miners may have some perks that others outside the country do not have.
We cant really deny into this fact but doesnt mean that they do have the control over the network they might ave big impact but not totally coming
to a point that it would be monopolized considering that China isnt the only place that do mine. No one control bitcoin and if someone does then its value wont really be the same on what we are seeing now.