Looking at China's medals so far, they are performing best in the swimming and weightlifting. Swimming rewards tall, muscled competitors. Weightlifting rewards squat, broad competitors. Neither of these are matches for the typical short, slender Chinese physique. By contrast: shooting, fencing, diving are natural matches for the 100% focus on medal-winning training that China promotes.
If there were an Olympic medal for undetectable doping, my opinion is that China would be a shoe-in for the gold.