From what I have seen of the driving test in the mainland, I believe it's fairly rigorous, these days, with computerised theory and practical elements that cover much the same things as the UK test.
The practical assessment is taken off-road in a driving school, which, I admit, does mean that newly licenced drivers on China's roads have absolutely no prior experience of traffic. However, the technical aspects of controling a vehicle are pretty well covered.
The two greatest failings, as I see them, are these :
1) A lot of people still buy their licences. Of the people I know who drive in the mainland, over half bought their licences. While most bought them some years ago, and there has been some suggestion that this practice has now become less common, I still know two people who bought their licences VERY recently. One of them had her licence bought for her by her father because she failed her test. Her driving instructor had told her that she was dangerous on the roads, which had put her off wanting to take the test again.
2) The first unwritten rule of driving in China is to throw the rule book out of the window. Drivers may have remembered the rules well enough to pass the computerised test, but that then bears no practical relation to actual conditions on the roads. Knowing what the rule book says about approaching junctions doesn't prepare a student for the reality of what a Chinese intersection is like, or how to stay alive in negotiating it. The only rule of thumb is to expect every other driver to go for any (even faintly viable) gap in traffic and to not be properly looking out for road threats. Remember this and adapt your road presence accordingly.
I had a tiny prang in the mainland, once, due in no small part to the sheer stupidity of a driver from the oncoming flow who thought it appropriate to do a U-turn across a six-lane highway in heavy traffic. We then yelled at each other for half an hour, each demanding that the other pay for the damage (as is the custom on the mainland), until a police officer turned up and threatened to tow our vehicles and impound them for a few days unless we settled the matter and cleared the road. Small bribe to the policeman and an agreement to meet our own costs sorted things out. Turns out the woman into who side I went didn't even have a licence, bought or otherwise.