How about on a per capita basis?
https://www.theguardian.com/world/2015/jan/06/tony-porter-su...
Or how about
1. In terms of quality and sophistication tech. US and Britain pioneered most of the surveillance tech.
2. Experience and age? We have decades head start on the chinese when it comes to tech surveillance.
3. We are more "connected" and a more urban society with surveillable data? Nearly 50% of china still lives in rural areas.