I can't comment on China. But the idea that most criminal trials result in convictions is not that surprising, and I suspect that it is probably true in the USA, Canada, England, and other western nations.
The part you may not be accounting for is that most criminal cases do not go to trial. Some cases get dismissed for lack of evidence, but in most criminal cases, the defendant takes a plea bargain.
Japan's criminal justice system is known for very lengthy pretrial detention. Defendants who may be innocent, or may be guilty of something lesser than what they are charged with, often give up and take a plea, because taking the case to trial could take years, and they won't get out on bail.
In the USA, in most states, the system is pretty simple: If you are white and you have money, you get to remain free while waiting for your case to go to trial. If you are not white and/or do not have money, you sit in jail while waiting for your case to go to trial.
Apparently, in Japan, they just keep most people in jail. And that puts massive pressure on the person to take a plea. You can sit in jail waiting for trial for two and a half years, and be found not guilty at a trial. But you won't get those two years back. You can pretty much forget about your job and your spouse...
BMK