I think America may be a bit of an exception actually since you guys elect your judges. That sounds ridiculous to me. It is like electing your doctor or your engineers. Some things simply are best left to technocrats.
That said, in the UK at least, you have the choice of five appeals before a final, conclusive say is given in your case.
Take for example Assange, the Wikileaks founder. It is difficult to find a more political example. He went up to the highest court. That final hearing was held in public, as all hearings are, it was televised, again as all hearings are, you can read the judicial decision, as with all judicial decision. No one was corrupted. You can't corrupt them, because there is complete transparency.
Now take the hacking scandal. At least 10 people have been imprisoned and are awaiting trial I think. Maddof is another example. We will see what comes out of Libor, etc. We don't live in a perfect world, but we are the closest to it I think.
In regards to your point about 20+ year sentence for a relatively minor crime, I think you will find that the media often sensationalises things to get attention. If you delve into these cases, by for example, reading the judicial decision which are available to everyone, you will most probably find that the decision if not to your agreement, is reasonable and justified.
To conclude with clearly showing that there is no comparison between America or the West and Russia, if you look at 1,000 cases, you are very likely to find way more non guilty verdicts than in 2 cases.