Neither I nor any of my family have been tried in China (I am guessing you haven't either), so I cannot comment on the legal system, but in reality, the legal system in the UK is not perfect either. There was a really good book released 2018 about how the legal system is broken here, if you are interested, it's a really good read:
Onto the topic of the extradition bill though, it specifically excludes extraditing politial dissidents, so it would not streamline the process. What I hear some people say that China will just make some excuses in other areas, which then I don't see the point, since kidnapping and disappearing people would surely be easier right, and since they can already do that, then why would they need the bill? But you know what the bill does allow HK to do, is to extradite a baby murderer to face charges of the crime he commited.
https://www.amazon.co.uk/Secret-Barrister-Stories-Law-Broken...
Onto the topic of the extradition bill though, it specifically excludes extraditing politial dissidents, so it would not streamline the process. What I hear some people say that China will just make some excuses in other areas, which then I don't see the point, since kidnapping and disappearing people would surely be easier right, and since they can already do that, then why would they need the bill? But you know what the bill does allow HK to do, is to extradite a baby murderer to face charges of the crime he commited.