"They're trained to properly identify targets before shooting, knowing that they will be required to justify their actions in court."
Obviously, they neither properly identified their target nor did they have to justify their actions in court.
I think the balance is about right and nothing like the USA. More importantly the jury of peers, in the coroners court, thought the Met Police failed on Health and Safety grounds but not the individual shooters.
The big difference is, there are fewer opportunities for armed police to screw this up. There are far fewer of them (heavily armed police are the exception, rather than the default) and they are not nearly needed as often (the citizenry is not as heavily armed). The policy that largely prevents the mistakes is what really helps, rather than having better armed police or better post-cockup inquiries (both of which, to me, seem fairly debatable).