I doubt there's any system in the world where it's officially the job of a prosecutor to "convict someone at all costs". It certainly isn't in the US. Nevertheless....
Most of the very real dynamics that affect all of our lives at a policy-making / systemic level are never official. If you think the official stuff is a reflection of reality ... I don't know how to finish this sentence. Safe from it being "official", it is very much the job of a prosecutor in the US to convict someone at all costs. This is common knowledge.
The Soviet Union is a perfect example of this. They had set up a proper republic. It had a constitution, elections, there were government posts etc. The problem was that the Party came first. The official that held the government post might've had the legal power, but in reality they were rubber stamps for the Party.
I know. I live in such country. But even here it is better for the prosecutor’s career with many convictions.
Conviction rates are surprisingly high in a lot of the first world.
I’m not sure what conclusion we should draw from that isolated fact. It can mean that people are convicted on too weak evidence, and it can mean that people are only put on trial when the evidence already is very strong.
I think we can look at the plea bargain rates and assume that most people do not have the resources to stand trial, and thus plea out whether or not the charges against them are valid.